2010
653.
Y Nakai, T Iye, S Kitagawa, K Ishida, S Kasahara, T Shibauchi, Y Matsuda, T Terashima
P 31 and A 75 s NMR evidence for a residual density of states at zero energy in superconducting BaFe2( As0.67P 0.33)2 Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 81, no. 2, 2010.
@article{Nakai2010d,
title = {P 31 and A 75 s NMR evidence for a residual density of states at zero energy in superconducting BaFe2( As0.67P 0.33)2},
author = {Y Nakai and T Iye and S Kitagawa and K Ishida and S Kasahara and T Shibauchi and Y Matsuda and T Terashima},
doi = {10.1103/PhysRevB.81.020503},
year = {2010},
date = {2010-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {81},
number = {2},
abstract = {P 31 and A 75 s NMR measurements were performed in superconducting BaFe2( As0.67P0.33)2 with Tc =30 K. The nuclear-spin-lattice relaxation rate T 1 -1 and the Knight shift in the normal state indicate the development of antiferromagnetic fluctuations, and T 1 -1 in the superconducting (SC) state decreases without a coherence peak just below Tc, as observed in (Ba1-x Kx) Fe2 As 2. In contrast to other iron arsenide superconductors, the T 1 -1 T behavior is observed below 4 K, indicating the presence of a residual density of states at zero energy. Our results suggest that strikingly different SC gaps appear in BaFe2 (As1-x Px)2despite a comparable Tc value, an analogous phase diagram, and similar Fermi surfaces to (Ba1-x Kx) Fe2 As2. © 2010 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
P 31 and A 75 s NMR measurements were performed in superconducting BaFe2( As0.67P0.33)2 with Tc =30 K. The nuclear-spin-lattice relaxation rate T 1 -1 and the Knight shift in the normal state indicate the development of antiferromagnetic fluctuations, and T 1 -1 in the superconducting (SC) state decreases without a coherence peak just below Tc, as observed in (Ba1-x Kx) Fe2 As 2. In contrast to other iron arsenide superconductors, the T 1 -1 T behavior is observed below 4 K, indicating the presence of a residual density of states at zero energy. Our results suggest that strikingly different SC gaps appear in BaFe2 (As1-x Px)2despite a comparable Tc value, an analogous phase diagram, and similar Fermi surfaces to (Ba1-x Kx) Fe2 As2. © 2010 The American Physical Society.
2009
652.
K Kitagawa, R Higashinaka, K Ishida, Y Maeno, M Takigawa
Erratum: High-temperature spin relaxation process in Dy2 Ti2 O7 probed by Ti47 -NQR Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 80, no. 22, 2009.
@article{Kitagawa2009,
title = {Erratum: High-temperature spin relaxation process in Dy2 Ti2 O7 probed by Ti47 -NQR},
author = {K Kitagawa and R Higashinaka and K Ishida and Y Maeno and M Takigawa},
doi = {10.1103/PhysRevB.80.229902},
year = {2009},
date = {2009-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {80},
number = {22},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
651.
S Kittaka, T Nakamura, Y Aono, S Yonezawa, K Ishida, Y Maeno
Angular dependence of the upper critical field of Sr2 RuO4 Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 80, no. 17, 2009.
@article{Kittaka2009,
title = {Angular dependence of the upper critical field of Sr2 RuO4},
author = {S Kittaka and T Nakamura and Y Aono and S Yonezawa and K Ishida and Y Maeno},
doi = {10.1103/PhysRevB.80.174514},
year = {2009},
date = {2009-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {80},
number = {17},
abstract = {One of the remaining issues concerning the spin-triplet superconductivity of Sr2 RuO4 is the strong limit of the in-plane upper critical field Hc2 at low temperatures. In this study, we clarified the dependence of Hc2 on the angle θ between the magnetic field and the ab plane at various temperatures, by precisely and accurately controlling the magnetic field direction. We revealed that, although the temperature dependence of Hc2 for |θ| ≥5°is well explained by the orbital pair-breaking effect, Hc2 (T) for |θ| <5°is clearly limited at low temperatures. We also revealed that the Hc2 limit for |θ| <5°is present not only at low temperatures but also at temperatures close to Tc. These features may provide additional hints for clarifying the origin of the Hc2 limit. Interestingly, if the anisotropic ratio in Sr2 RuO4 is assumed to depend on temperature, the observed angular dependence of Hc2 is reproduced better at lower temperature with an effective-mass model for an anisotropic three-dimensional superconductor. We discuss the observed behavior of Hc2 based on existing theories. © 2009 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
One of the remaining issues concerning the spin-triplet superconductivity of Sr2 RuO4 is the strong limit of the in-plane upper critical field Hc2 at low temperatures. In this study, we clarified the dependence of Hc2 on the angle θ between the magnetic field and the ab plane at various temperatures, by precisely and accurately controlling the magnetic field direction. We revealed that, although the temperature dependence of Hc2 for |θ| ≥5°is well explained by the orbital pair-breaking effect, Hc2 (T) for |θ| <5°is clearly limited at low temperatures. We also revealed that the Hc2 limit for |θ| <5°is present not only at low temperatures but also at temperatures close to Tc. These features may provide additional hints for clarifying the origin of the Hc2 limit. Interestingly, if the anisotropic ratio in Sr2 RuO4 is assumed to depend on temperature, the observed angular dependence of Hc2 is reproduced better at lower temperature with an effective-mass model for an anisotropic three-dimensional superconductor. We discuss the observed behavior of Hc2 based on existing theories. © 2009 The American Physical Society.
650.
F Nakamura, R Nakai, T Takemoto, M Sakaki, T Suzuki, P L Alireza, S Nakatsuji, Y Maeno
Anisotropic giant magnetoresistance near the Mott transition in pressurized Ca2 RuO4 Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 80, no. 19, 2009.
@article{Nakamura2009,
title = {Anisotropic giant magnetoresistance near the Mott transition in pressurized Ca2 RuO4},
author = {F Nakamura and R Nakai and T Takemoto and M Sakaki and T Suzuki and P L Alireza and S Nakatsuji and Y Maeno},
doi = {10.1103/PhysRevB.80.193103},
year = {2009},
date = {2009-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {80},
number = {19},
abstract = {We have observed an anisotropic and giant magnetoresistance (MR) in the 4d -electron Mott transition system of Ca2 RuO4. On the border of the Mott transition (∼2GPa), the MR effect at ∼10T reaches ∼-55% at TC for longitudinal and ∼+120% at low temperatures for the transverse effects. The negative MR is most likely interpreted as a reduction in a ferromagnetic (FM) fluctuation at TC. In contrast, the large positive effect is actually rare and is characteristic of the mixed state where the FM metallic islands are flecked with the insulating phases. We discuss the reason of the peculiar MR from the viewpoint of the "anisotropic magnetism," the "tunnel MR," and the "orbital physics." © 2009 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We have observed an anisotropic and giant magnetoresistance (MR) in the 4d -electron Mott transition system of Ca2 RuO4. On the border of the Mott transition (∼2GPa), the MR effect at ∼10T reaches ∼-55% at TC for longitudinal and ∼+120% at low temperatures for the transverse effects. The negative MR is most likely interpreted as a reduction in a ferromagnetic (FM) fluctuation at TC. In contrast, the large positive effect is actually rare and is characteristic of the mixed state where the FM metallic islands are flecked with the insulating phases. We discuss the reason of the peculiar MR from the viewpoint of the "anisotropic magnetism," the "tunnel MR," and the "orbital physics." © 2009 The American Physical Society.
649.
R Ciancio, H Pettersson, J Börjesson, S Lopatin, R Fittipaldi, A Vecchione, S Kittaka, Y Maeno, S Pace, E Olsson
Atomic structure of functional interfaces in Sr2 RuO4/Sr3 Ru2 O7 eutectic crystals Journal Article
In: Applied Physics Letters, vol. 95, no. 14, 2009.
@article{Ciancio2009,
title = {Atomic structure of functional interfaces in Sr2 RuO4/Sr3 Ru2 O7 eutectic crystals},
author = {R Ciancio and H Pettersson and J Börjesson and S Lopatin and R Fittipaldi and A Vecchione and S Kittaka and Y Maeno and S Pace and E Olsson},
doi = {10.1063/1.3243691},
year = {2009},
date = {2009-01-01},
journal = {Applied Physics Letters},
volume = {95},
number = {14},
abstract = {Sr2 RuO4/Sr3 Ru2 O7 eutectic system is investigated by transmission electron microscopy (TEM) and high angle annular dark field scanning TEM (STEM). The Sr2 RuO4 / Sr3 Ru2 O7 lamellar structure allows studying tunneling and proximity effects between spin-triplet superconductor Sr2 RuO4 and metamagnetic normal metal Sr3 Ru2 O7. Our analyses reveal two typologies of interfaces within the eutectic: interfaces parallel to the growth direction are sharp and defect-free whereas interfaces perpendicular to the growth direction appear wavy and decorated with Ru precipitates. These results indicate that interfaces parallel to the growth direction are the best candidates for Sr2 RuO4 / Sr3 Ru2 O7 natural junctions to study the unusual superconductivity of Sr2 RuO4. © 2009 American Institute of Physics.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Sr2 RuO4/Sr3 Ru2 O7 eutectic system is investigated by transmission electron microscopy (TEM) and high angle annular dark field scanning TEM (STEM). The Sr2 RuO4 / Sr3 Ru2 O7 lamellar structure allows studying tunneling and proximity effects between spin-triplet superconductor Sr2 RuO4 and metamagnetic normal metal Sr3 Ru2 O7. Our analyses reveal two typologies of interfaces within the eutectic: interfaces parallel to the growth direction are sharp and defect-free whereas interfaces perpendicular to the growth direction appear wavy and decorated with Ru precipitates. These results indicate that interfaces parallel to the growth direction are the best candidates for Sr2 RuO4 / Sr3 Ru2 O7 natural junctions to study the unusual superconductivity of Sr2 RuO4. © 2009 American Institute of Physics.
648.
H Yamaguchi, S Kimura, M Hagiwara, Y Nambu, S Nakatsuji, Y Maeno, K Kindo
High-field and multifrequency esr in the two-dimensional triangular lattice antiferromagnet niga2s4 Journal Article
In: Applied Magnetic Resonance, vol. 36, no. 2-4, pp. 285-289, 2009.
@article{Yamaguchi2009285,
title = {High-field and multifrequency esr in the two-dimensional triangular lattice antiferromagnet niga2s4},
author = {H Yamaguchi and S Kimura and M Hagiwara and Y Nambu and S Nakatsuji and Y Maeno and K Kindo},
doi = {10.1007/s00723-009-0017-3},
year = {2009},
date = {2009-01-01},
journal = {Applied Magnetic Resonance},
volume = {36},
number = {2-4},
pages = {285-289},
abstract = {We report the experimental results of electron spin resonance in high magnetic fields up to about 53 T on the quasi-two-dimensional triangular lattice antiferromagnet NiGa2S4. The temperature dependence of the resonance field at 584.8 GHz shows a steep change below about 30 K, indicating a development of the short-range correlation. The frequency dependence of the resonance field at the lowest temperature for Hpipepipec is explained by one of the helical resonance modes. These experimental results suggest that the short-range order is well developed at low temperatures, and the resonance mode is described by a conventional spin wave theory. © Springer 2009.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report the experimental results of electron spin resonance in high magnetic fields up to about 53 T on the quasi-two-dimensional triangular lattice antiferromagnet NiGa2S4. The temperature dependence of the resonance field at 584.8 GHz shows a steep change below about 30 K, indicating a development of the short-range correlation. The frequency dependence of the resonance field at the lowest temperature for Hpipepipec is explained by one of the helical resonance modes. These experimental results suggest that the short-range order is well developed at low temperatures, and the resonance mode is described by a conventional spin wave theory. © Springer 2009.
647.
H Kambara, S Kashiwaya, H Yaguchi, Y Asano, Y Tanaka, Y Maeno
Chiral superconducting phase transition in 3-K phase of Sr2RuO4 Journal Article
In: Physica C: Superconductivity and its Applications, vol. 469, no. 15-20, pp. 1030-1033, 2009.
@article{Kambara20091030,
title = {Chiral superconducting phase transition in 3-K phase of Sr2RuO4},
author = {H Kambara and S Kashiwaya and H Yaguchi and Y Asano and Y Tanaka and Y Maeno},
doi = {10.1016/j.physc.2009.05.176},
year = {2009},
date = {2009-01-01},
journal = {Physica C: Superconductivity and its Applications},
volume = {469},
number = {15-20},
pages = {1030-1033},
abstract = {We have investigated the transports of micro-fabricated sample of 3-K phase superconductivity (Tc ∼ 3 K) in Sr2RuO4-Ru eutectic system in order to clarify the pairing symmetry. Up to now, pure Sr2RuO4 (Tc = 1.5 K: 1.5-K phase) is widely recognized to be a spin-triplet odd-parity superconductor. However, the enhancement mechanism of Tc up to 3 K and the pairing symmetry of the 3-K phase have not been cleared yet. By using micro fabrication technique with focused ion beam, we have succeeded to extract individual superconducting channels for the 3-K phase in which only a few pieces of Ru inclusions are contained. Multiple kink structures observed in differential resistance-current (dV/dI - I) characteristics indicate serially connected superconducting filaments in the 3-K phase. We confirm that the 3-K phase is an odd-parity superconductor similar to pure Sr2RuO4 from the monotonous temperature dependence of the critical currents. In addition, we observed a quite unusual hysteresis in dV/dI - I below 2 K, which suggests the internal degrees of freedom in the superconducting state: the most probably the chiral p-wave state. © 2009 Elsevier B.V. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We have investigated the transports of micro-fabricated sample of 3-K phase superconductivity (Tc ∼ 3 K) in Sr2RuO4-Ru eutectic system in order to clarify the pairing symmetry. Up to now, pure Sr2RuO4 (Tc = 1.5 K: 1.5-K phase) is widely recognized to be a spin-triplet odd-parity superconductor. However, the enhancement mechanism of Tc up to 3 K and the pairing symmetry of the 3-K phase have not been cleared yet. By using micro fabrication technique with focused ion beam, we have succeeded to extract individual superconducting channels for the 3-K phase in which only a few pieces of Ru inclusions are contained. Multiple kink structures observed in differential resistance-current (dV/dI - I) characteristics indicate serially connected superconducting filaments in the 3-K phase. We confirm that the 3-K phase is an odd-parity superconductor similar to pure Sr2RuO4 from the monotonous temperature dependence of the critical currents. In addition, we observed a quite unusual hysteresis in dV/dI - I below 2 K, which suggests the internal degrees of freedom in the superconducting state: the most probably the chiral p-wave state. © 2009 Elsevier B.V. All rights reserved.
646.
P J Baker, R J Ormeno, C E Gough, Z Q Mao, S Nishizaki, Y Maeno
Microwave surface impedance measurements of Sr2 RuO4: The effect of impurities Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 80, no. 11, 2009.
@article{Baker2009,
title = {Microwave surface impedance measurements of Sr2 RuO4: The effect of impurities},
author = {P J Baker and R J Ormeno and C E Gough and Z Q Mao and S Nishizaki and Y Maeno},
doi = {10.1103/PhysRevB.80.115126},
year = {2009},
date = {2009-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {80},
number = {11},
abstract = {The temperature, purity, and frequency dependence of the real and imaginary components of the complex surface impedance of three single crystals of the proposed p -wave superconductor Sr2 RuO4, with Tc values of 1.40, 1.24, and 0.74 K, have been measured over a range of microwave frequencies from 4-16 GHz down to 100 mK. The unusual superconducting microwave properties can be described by a multiband, two-fluid model consistent with electron relaxation times remaining largely unchanged on entering the superconducting state and energy gaps on all bands having the same temperature dependence. In addition, the model is consistent with nonmagnetic impurity scattering strongly suppressing the superconducting fractions leading to large residual losses at low temperatures and an increase in penetration depth. Model independent derivations of the complex microwave conductivity are shown to be largely consistent with such a scenario. © 2009 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The temperature, purity, and frequency dependence of the real and imaginary components of the complex surface impedance of three single crystals of the proposed p -wave superconductor Sr2 RuO4, with Tc values of 1.40, 1.24, and 0.74 K, have been measured over a range of microwave frequencies from 4-16 GHz down to 100 mK. The unusual superconducting microwave properties can be described by a multiband, two-fluid model consistent with electron relaxation times remaining largely unchanged on entering the superconducting state and energy gaps on all bands having the same temperature dependence. In addition, the model is consistent with nonmagnetic impurity scattering strongly suppressing the superconducting fractions leading to large residual losses at low temperatures and an increase in penetration depth. Model independent derivations of the complex microwave conductivity are shown to be largely consistent with such a scenario. © 2009 The American Physical Society.
645.
R Ciancio, J Börjesson, H Pettersson, R Fittipaldi, D Zola, A Vecchione, M Polichetti, S Kittaka, Y Maeno, S Pace, E Olsson
Toward intrinsic functionalities of bilayered ruthenate Sr3 Ru2 O7 Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 80, no. 5, 2009.
@article{Ciancio2009b,
title = {Toward intrinsic functionalities of bilayered ruthenate Sr3 Ru2 O7},
author = {R Ciancio and J Börjesson and H Pettersson and R Fittipaldi and D Zola and A Vecchione and M Polichetti and S Kittaka and Y Maeno and S Pace and E Olsson},
doi = {10.1103/PhysRevB.80.054110},
year = {2009},
date = {2009-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {80},
number = {5},
abstract = {Polymorphic materials are known for being prone to intergrowth. Remarkable examples are strontium ruthenates whose properties are dramatically tuned by impurities and disorder. In particular, Sr3 Ru2 O7 shows a strong variation in transport and magnetic properties depending on synthesis process. It is therefore crucial to correlate atomic structure and properties to identify the functionalities of individual nanostructural constituents. We report a comparative study between Sr3 Ru2 O7 crystals grown as single phase and in Sr3 Ru2 O7 -Sr2 RuO4 eutectics. Our analysis by transmission electron microscopy reveals that Sr3 Ru2 O7 domains of the eutectic have a significantly lower level of impurities compared to Sr3 Ru2 O7 single-phase crystals, where intergrowths of Sr4 Ru3 O10 and SrRuO3 phase are seen. This is confirmed by magnetic measurements. These results identify the eutectic solidification as a fruitful way to grow highly pure crystals of polymorphic materials which, in combination with recent technological developments allowing the extraction of embedded features of crystals, opens a pathway for understanding of their physical properties and applications. © 2009 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Polymorphic materials are known for being prone to intergrowth. Remarkable examples are strontium ruthenates whose properties are dramatically tuned by impurities and disorder. In particular, Sr3 Ru2 O7 shows a strong variation in transport and magnetic properties depending on synthesis process. It is therefore crucial to correlate atomic structure and properties to identify the functionalities of individual nanostructural constituents. We report a comparative study between Sr3 Ru2 O7 crystals grown as single phase and in Sr3 Ru2 O7 -Sr2 RuO4 eutectics. Our analysis by transmission electron microscopy reveals that Sr3 Ru2 O7 domains of the eutectic have a significantly lower level of impurities compared to Sr3 Ru2 O7 single-phase crystals, where intergrowths of Sr4 Ru3 O10 and SrRuO3 phase are seen. This is confirmed by magnetic measurements. These results identify the eutectic solidification as a fruitful way to grow highly pure crystals of polymorphic materials which, in combination with recent technological developments allowing the extraction of embedded features of crystals, opens a pathway for understanding of their physical properties and applications. © 2009 The American Physical Society.
644.
T Sudayama, Y Wakisaka, K Takubo, T Mizokawa, W Kobayashi, I Terasaki, S Tanaka, Y Maeno, M Arita, H Namatame, M Taniguchi
Bulk-sensitive photoemission study of A Cu3 Ru4 O12 (A=Ca, Na, and La) with heavy-fermion behavior Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 80, no. 7, 2009.
@article{Sudayama2009,
title = {Bulk-sensitive photoemission study of A Cu3 Ru4 O12 (A=Ca, Na, and La) with heavy-fermion behavior},
author = {T Sudayama and Y Wakisaka and K Takubo and T Mizokawa and W Kobayashi and I Terasaki and S Tanaka and Y Maeno and M Arita and H Namatame and M Taniguchi},
doi = {10.1103/PhysRevB.80.075113},
year = {2009},
date = {2009-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {80},
number = {7},
abstract = {We have studied the d -electron heavy-fermion states in A Cu3 Ru4 O12 (A=Ca, Na, and La) using x-ray photoemission spectroscopy and high-resolution photoemission spectroscopy at bulk-sensitive photon energy (7 eV). The bulk-sensitive photoemission measurements for A=Ca, Na, and La show that a resonancelike structure within a pseudogap commonly evolves in the low-temperature range where the Kadowaki-Woods relation holds. The origin of the resonancelike peak and the heavy-fermion behavior is basically attributed to the hybridization between the Cu3d and Ru4d orbitals. The A -site substitution controls the filling of the Cu3d and Ru 4d hybridized bands. Interestingly, while the resonancelike peak position roughly follows the rigid-band shift for A=Na and La, the resonancelike peak deviating from the rigid-band behavior is located just at the Fermi level as expected in a Kondo system. The difference in the resonancelike peak near the Fermi level is correlated with that in the Cu2p core-level spectra. © 2009 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We have studied the d -electron heavy-fermion states in A Cu3 Ru4 O12 (A=Ca, Na, and La) using x-ray photoemission spectroscopy and high-resolution photoemission spectroscopy at bulk-sensitive photon energy (7 eV). The bulk-sensitive photoemission measurements for A=Ca, Na, and La show that a resonancelike structure within a pseudogap commonly evolves in the low-temperature range where the Kadowaki-Woods relation holds. The origin of the resonancelike peak and the heavy-fermion behavior is basically attributed to the hybridization between the Cu3d and Ru4d orbitals. The A -site substitution controls the filling of the Cu3d and Ru 4d hybridized bands. Interestingly, while the resonancelike peak position roughly follows the rigid-band shift for A=Na and La, the resonancelike peak deviating from the rigid-band behavior is located just at the Fermi level as expected in a Kondo system. The difference in the resonancelike peak near the Fermi level is correlated with that in the Cu2p core-level spectra. © 2009 The American Physical Society.
643.
S Tanaka, H Takatsu, S Yonezawa, Y Maeno
Suppression of the mass enhancement in CaCu3 Ru4 O12 Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 80, no. 3, 2009.
@article{Tanaka2009,
title = {Suppression of the mass enhancement in CaCu3 Ru4 O12},
author = {S Tanaka and H Takatsu and S Yonezawa and Y Maeno},
doi = {10.1103/PhysRevB.80.035113},
year = {2009},
date = {2009-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {80},
number = {3},
abstract = {We have investigated heavy-fermion behavior of the transition-metal oxides A Cu3 Ru4 O12 (A=Na,Ca,La, and their mixtures). It has been known that CaCu3 Ru4 O12 exhibits Kondo-like behavior attributable to Cu2+ 3d electrons, similar to that of some Ce-based heavy-fermion systems. However, we find striking suppression of the mass enhancement in CaCu3 Ru4 O12, in which the Kondo-type effect is most pronounced. Such decrease in the density of states is reminiscent of the coherent-gap formation in Kondo lattice systems. Nevertheless, the behavior can not be interpreted within the conventional Kondo picture with localized moments because the Cu electrons are apparently itinerant. The present results indicate the importance of the duality of localized and itinerant nature, found also in some other d -electron systems which exhibit the Kondo-like behavior. © 2009 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We have investigated heavy-fermion behavior of the transition-metal oxides A Cu3 Ru4 O12 (A=Na,Ca,La, and their mixtures). It has been known that CaCu3 Ru4 O12 exhibits Kondo-like behavior attributable to Cu2+ 3d electrons, similar to that of some Ce-based heavy-fermion systems. However, we find striking suppression of the mass enhancement in CaCu3 Ru4 O12, in which the Kondo-type effect is most pronounced. Such decrease in the density of states is reminiscent of the coherent-gap formation in Kondo lattice systems. Nevertheless, the behavior can not be interpreted within the conventional Kondo picture with localized moments because the Cu electrons are apparently itinerant. The present results indicate the importance of the duality of localized and itinerant nature, found also in some other d -electron systems which exhibit the Kondo-like behavior. © 2009 The American Physical Society.
642.
T M Rice, M Sigrist, Y Maeno
Focus on superconductors with exotic symmetries Journal Article
In: New Journal of Physics, vol. 11, 2009.
@article{Rice2009,
title = {Focus on superconductors with exotic symmetries},
author = {T M Rice and M Sigrist and Y Maeno},
doi = {10.1088/1367-2630/11/5/055052},
year = {2009},
date = {2009-01-01},
journal = {New Journal of Physics},
volume = {11},
abstract = {Significant efforts are being made to develop semiconductors with exotic pairing symmetries. The significance of these exotic semiconductors with unconventional symmetry is that their pairing is of electronic origin. These semiconductors are freed from the limitations of low transition temperatures are are combined with the photon driven conventional semiconductors. The two main classes of these semiconductors, including heavy ferminion and organic semiconductors have significantly low intrinsic energy scales that lead to low temperature scales. The third class exotic semiconductors contain the small number of superconducting transition metal compounds with exotic pairing symmetry. The most studied exotic semiconductors include high Tc cuprates, iron pnictides, and strontium ruthenate that is closely related to superfluid 3He.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Significant efforts are being made to develop semiconductors with exotic pairing symmetries. The significance of these exotic semiconductors with unconventional symmetry is that their pairing is of electronic origin. These semiconductors are freed from the limitations of low transition temperatures are are combined with the photon driven conventional semiconductors. The two main classes of these semiconductors, including heavy ferminion and organic semiconductors have significantly low intrinsic energy scales that lead to low temperature scales. The third class exotic semiconductors contain the small number of superconducting transition metal compounds with exotic pairing symmetry. The most studied exotic semiconductors include high Tc cuprates, iron pnictides, and strontium ruthenate that is closely related to superfluid 3He.
641.
S Kittaka, T Nakamura, H Yaguchi, S Yonezawa, Y Maeno
Spatial development of superconductivity in the Sr 2Ruo 4-Ru eutectic system Journal Article
In: Journal of the Physical Society of Japan, vol. 78, no. 6, 2009.
@article{Kittaka2009b,
title = {Spatial development of superconductivity in the Sr 2Ruo 4-Ru eutectic system},
author = {S Kittaka and T Nakamura and H Yaguchi and S Yonezawa and Y Maeno},
doi = {10.1143/JPSJ.78.064703},
year = {2009},
date = {2009-01-01},
journal = {Journal of the Physical Society of Japan},
volume = {78},
number = {6},
abstract = {We have clarified how the enhanced superconductivity, often referred to as the 3-K phase superconductivity, develops in the Sr 2Ruo 4-Ru eutectic system. From the detailed ac and dc susceptibility measurements on well-characterized crystals, we revealed strongly anisotropic shielding, governed by the direction of the screening current dominated within the RuO 2 plane rather than by the orientation of the Ru lamellae. The onset temperature of the 3-K phase superconductivity probed by diamagnetic screening is as high as 3.5 K. The temperature dependence of the diamagnetic shielding above around 2K is well ascribed by the interfacial screening around each Ru lamella. Below around 2K, the rapid development of the shielding fraction as well as its peculiar response to ac and dc magnetic fields are explained by the formation of the Josephson network consisting of inter-lamellar supercurrents. © 2009 The Physical Society of Japan.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We have clarified how the enhanced superconductivity, often referred to as the 3-K phase superconductivity, develops in the Sr 2Ruo 4-Ru eutectic system. From the detailed ac and dc susceptibility measurements on well-characterized crystals, we revealed strongly anisotropic shielding, governed by the direction of the screening current dominated within the RuO 2 plane rather than by the orientation of the Ru lamellae. The onset temperature of the 3-K phase superconductivity probed by diamagnetic screening is as high as 3.5 K. The temperature dependence of the diamagnetic shielding above around 2K is well ascribed by the interfacial screening around each Ru lamella. Below around 2K, the rapid development of the shielding fraction as well as its peculiar response to ac and dc magnetic fields are explained by the formation of the Josephson network consisting of inter-lamellar supercurrents. © 2009 The Physical Society of Japan.
640.
H Takatsu, H Yoshizawa, S Yonezawa, Y Maeno
Critical behavior of the metallic triangular-lattice Heisenberg antiferromagnet PdCrO2 Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 79, no. 10, 2009.
@article{Takatsu2009,
title = {Critical behavior of the metallic triangular-lattice Heisenberg antiferromagnet PdCrO2},
author = {H Takatsu and H Yoshizawa and S Yonezawa and Y Maeno},
doi = {10.1103/PhysRevB.79.104424},
year = {2009},
date = {2009-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {79},
number = {10},
abstract = {We report physical properties of the conductive magnet PdCrO2 consisting of a layered structure with a triangular lattice of Cr3+ ions (S=3/2). We confirmed an antiferromagnetic transition at TN =37.5/K by means of specific heat, electrical resistivity, magnetic susceptibility, and neutron-scattering measurements. The critical behavior in the specific heat persists in an unusually wide temperature range above TN. This fact implies that spin correlations develop even at a much higher temperature than TN. The observed sublinear temperature dependence of the resistivity above TN is also attributed to the short-range correlations among the frustrated spins. While the critical exponent for the magnetization agrees reasonably with the prediction of the relevant model, that for the specific heat evaluated in the wide temperature range differs substantially from the prediction. © 2009 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report physical properties of the conductive magnet PdCrO2 consisting of a layered structure with a triangular lattice of Cr3+ ions (S=3/2). We confirmed an antiferromagnetic transition at TN =37.5/K by means of specific heat, electrical resistivity, magnetic susceptibility, and neutron-scattering measurements. The critical behavior in the specific heat persists in an unusually wide temperature range above TN. This fact implies that spin correlations develop even at a much higher temperature than TN. The observed sublinear temperature dependence of the resistivity above TN is also attributed to the short-range correlations among the frustrated spins. While the critical exponent for the magnetization agrees reasonably with the prediction of the relevant model, that for the specific heat evaluated in the wide temperature range differs substantially from the prediction. © 2009 The American Physical Society.
639.
A Shimoyamada, K Ishizaka, S Tsuda, S Nakatsuji, Y Maeno, S Shin
Strong mass renormalization at a local momentum space in multiorbital Ca1.8Sr0.2RuO4 Journal Article
In: Physical Review Letters, vol. 102, no. 8, 2009.
@article{Shimoyamada2009,
title = {Strong mass renormalization at a local momentum space in multiorbital Ca1.8Sr0.2RuO4},
author = {A Shimoyamada and K Ishizaka and S Tsuda and S Nakatsuji and Y Maeno and S Shin},
doi = {10.1103/PhysRevLett.102.086401},
year = {2009},
date = {2009-01-01},
journal = {Physical Review Letters},
volume = {102},
number = {8},
abstract = {We have studied the mass renormalization in Ca2-xSrxRuO4 (x=0.2) using high-resolution angle-resolved photoemission spectroscopy. We observed precise band dispersions near the Fermi level (EF) and the corresponding Fermi surfaces. A characteristic flat band with ∼4meV dispersion accompanying sharp quasiparticle (QP) peaks shows up in a limited momentum region around (π, 0). The QP peak rapidly evolves below the crossover temperature T* 20K, which agrees well with the mass enhancement behavior indicated by thermal, magnetic, and transport properties. We discuss the origin of the mass renormalization in relation to the local flat band at (π, 0) possibly derived from the γ (dxy) band. © 2009 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We have studied the mass renormalization in Ca2-xSrxRuO4 (x=0.2) using high-resolution angle-resolved photoemission spectroscopy. We observed precise band dispersions near the Fermi level (EF) and the corresponding Fermi surfaces. A characteristic flat band with ∼4meV dispersion accompanying sharp quasiparticle (QP) peaks shows up in a limited momentum region around (π, 0). The QP peak rapidly evolves below the crossover temperature T* 20K, which agrees well with the mass enhancement behavior indicated by thermal, magnetic, and transport properties. We discuss the origin of the mass renormalization in relation to the local flat band at (π, 0) possibly derived from the γ (dxy) band. © 2009 The American Physical Society.
638.
S Tanaka, N Shimazui, H Takatsu, S Yonezawa, Y Maeno
Heavy-mass behavior of ordered perovskites ACu 3Ru 4O 12 (A = Na, Ca, La) Journal Article
In: Journal of the Physical Society of Japan, vol. 78, no. 2, 2009.
@article{Tanaka2009b,
title = {Heavy-mass behavior of ordered perovskites ACu 3Ru 4O 12 (A = Na, Ca, La)},
author = {S Tanaka and N Shimazui and H Takatsu and S Yonezawa and Y Maeno},
doi = {10.1143/JPSJ.78.024706},
year = {2009},
date = {2009-01-01},
journal = {Journal of the Physical Society of Japan},
volume = {78},
number = {2},
abstract = {We synthesized ACu 3Ru 4O 12 (A = Na, Na 0.5Ca 0.5, Ca, Ca 0.5La 0.5, La) and measured their DC magnetization, AC susceptibility, specific heat, and resistivity, in order to investigate the effects of the hetero-valent substitution. A broad peak in the DC magnetization around 200K was observed only in CaCu 3Ru 4O 12, suggesting the Kondo effect due to localized Cu 2+ ions. However, the electronic specific heat coefficients γ exhibit large values not only for CaCu 3Ru 4O 12 but also for all the other samples. Moreover, the Wilson ratio and the Kadowaki-Woods ratio of our samples are all similar to the values of other heavy-fermion compounds. These results question the Kondo effect as the dominant origin of the mass enhancement, and rather indicate the importance of correlations among itinerant Ru electrons. ©2009 The Physical Society of Japan.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We synthesized ACu 3Ru 4O 12 (A = Na, Na 0.5Ca 0.5, Ca, Ca 0.5La 0.5, La) and measured their DC magnetization, AC susceptibility, specific heat, and resistivity, in order to investigate the effects of the hetero-valent substitution. A broad peak in the DC magnetization around 200K was observed only in CaCu 3Ru 4O 12, suggesting the Kondo effect due to localized Cu 2+ ions. However, the electronic specific heat coefficients γ exhibit large values not only for CaCu 3Ru 4O 12 but also for all the other samples. Moreover, the Wilson ratio and the Kadowaki-Woods ratio of our samples are all similar to the values of other heavy-fermion compounds. These results question the Kondo effect as the dominant origin of the mass enhancement, and rather indicate the importance of correlations among itinerant Ru electrons. ©2009 The Physical Society of Japan.
637.
R Flttipaldi, Y Maeno, A Vecchione
Structure, morphology and composition ot natural junctions of Sr2Ru04-Sr3Ru207 eutectic crystals Journal Article
In: Journal of Physics Condensed Matter, vol. 21, 2009.
@article{Flttipaldi2009,
title = {Structure, morphology and composition ot natural junctions of Sr2Ru04-Sr3Ru207 eutectic crystals},
author = {R Flttipaldi and Y Maeno and A Vecchione},
doi = {10.1088/0953-8984/21/25/254211},
year = {2009},
date = {2009-01-01},
journal = {Journal of Physics Condensed Matter},
volume = {21},
abstract = {A detailed study of morphological, compositional and structural aspects of Sr2RuO4-Sr3Ru2O7 eutectic crystals is reported. The stoichiometry of the phases that compose the crystals and how they are arranged in the crystals are studied. Understanding the behavior at the Sr2Ru04-Sr3Ru207 interface represents a necessary prerequisite for the analysis of the experimental results on the transport properties recently reported in the literature. © 2009 10P Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
A detailed study of morphological, compositional and structural aspects of Sr2RuO4-Sr3Ru2O7 eutectic crystals is reported. The stoichiometry of the phases that compose the crystals and how they are arranged in the crystals are studied. Understanding the behavior at the Sr2Ru04-Sr3Ru207 interface represents a necessary prerequisite for the analysis of the experimental results on the transport properties recently reported in the literature. © 2009 10P Publishing Ltd.
636.
H Yaguchi, S Kittaka, Y Maeno
Enhancement of interfacial superconductivity in the eutectic system Sr 2RuO4-Ru by uniaxial pressure Conference
vol. 150, no. 5, 2009.
@conference{Yaguchi2009,
title = {Enhancement of interfacial superconductivity in the eutectic system Sr 2RuO4-Ru by uniaxial pressure},
author = {H Yaguchi and S Kittaka and Y Maeno},
doi = {10.1088/1742-6596/150/5/052285},
year = {2009},
date = {2009-01-01},
journal = {Journal of Physics: Conference Series},
volume = {150},
number = {5},
abstract = {We have investigated effects of uniaxial pressure on superconductivity in the 3-K phase in the eutectic system Sr2RuO4-Ru. We have found a large enhancement of 3-K phase superconductivity particularly in volume fraction for both in-plane pressure P∥ ab and the c-axis pressure P ∥ c in contrast to expectations for the 1.5-K phase in pure Sr2RuO 4. Surprisingly, the effect of the in-plane pressure is even greater than that of the c-axis pressure. This could be related to the origin of the 3-K phase. © 2009 IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
We have investigated effects of uniaxial pressure on superconductivity in the 3-K phase in the eutectic system Sr2RuO4-Ru. We have found a large enhancement of 3-K phase superconductivity particularly in volume fraction for both in-plane pressure P∥ ab and the c-axis pressure P ∥ c in contrast to expectations for the 1.5-K phase in pure Sr2RuO 4. Surprisingly, the effect of the in-plane pressure is even greater than that of the c-axis pressure. This could be related to the origin of the 3-K phase. © 2009 IOP Publishing Ltd.
635.
H Takatsu, H Yoshizawa, Y Maeno
vol. 145, no. 1, 2009.
@conference{Takatsu2009b,
title = {Comparative study of conductive delafossites with and without frustrated spins on a triangular lattice, PdMO2 (M = Cr; Co)},
author = {H Takatsu and H Yoshizawa and Y Maeno},
doi = {10.1088/1742-6596/145/1/012046},
year = {2009},
date = {2009-01-01},
journal = {Journal of Physics: Conference Series},
volume = {145},
number = {1},
abstract = {We report a comparative study of the conductive oxides PdMO2 (M = Cr, Co) consisting of a layered structure with a triangular lattice of M 3+ ions: PdCrO2 (S = 3=2) is magnetically active showing an antiferromagnetic (AF) transition at TN≅37:5 K, whereas PdCoO 2 (S = 0) is not magnetically active. Both compounds exhibit metallic conductivity down to low temperatures, but the temperature dependence of the resistivity is quite different reflecting the difference in their magnetic properties. Especially, the resistivity of PdCrO2 exhibits strong sub-linear temperature dependence in a wide temperature range above TN. Such dependence is markedly different from that of ordinary magnetic metals with non-frustrated localized spin moments. The estimated entropy at TN is substantially smaller than that expected for a system with S = 3=2, suggesting that the spin correlations still remain much above TN. These facts indicate that it is the short-range correlations of frustrated spins that leads to the unusual sub-linear temperature dependence of the resistivity. © 2009 IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
We report a comparative study of the conductive oxides PdMO2 (M = Cr, Co) consisting of a layered structure with a triangular lattice of M 3+ ions: PdCrO2 (S = 3=2) is magnetically active showing an antiferromagnetic (AF) transition at TN≅37:5 K, whereas PdCoO 2 (S = 0) is not magnetically active. Both compounds exhibit metallic conductivity down to low temperatures, but the temperature dependence of the resistivity is quite different reflecting the difference in their magnetic properties. Especially, the resistivity of PdCrO2 exhibits strong sub-linear temperature dependence in a wide temperature range above TN. Such dependence is markedly different from that of ordinary magnetic metals with non-frustrated localized spin moments. The estimated entropy at TN is substantially smaller than that expected for a system with S = 3=2, suggesting that the spin correlations still remain much above TN. These facts indicate that it is the short-range correlations of frustrated spins that leads to the unusual sub-linear temperature dependence of the resistivity. © 2009 IOP Publishing Ltd.
634.
M Kriener, T Muranaka, Z-A Ren, J Kato, J Akimitsu, Y Maeno
Superconductivity of hexagonal heavily-boron doped silicon carbide Conference
vol. 150, no. 5, 2009.
@conference{Kriener2009,
title = {Superconductivity of hexagonal heavily-boron doped silicon carbide},
author = {M Kriener and T Muranaka and Z-A Ren and J Kato and J Akimitsu and Y Maeno},
doi = {10.1088/1742-6596/150/5/052130},
year = {2009},
date = {2009-01-01},
journal = {Journal of Physics: Conference Series},
volume = {150},
number = {5},
abstract = {In 2004 the discovery of superconductivity in heavily boron-doped diamond (C:B) led to an increasing interest in the superconducting phases of wide-gap semiconductors. Subsequently superconductivity was found in heavily boron-doped cubic silicon (Si:B) and recently in the stochiometric "mixture" of heavily boron-doped silicon carbide (SiC:B). The latter system surprisingly exhibits type-I superconductivity in contrast to the type-II superconductors C:B and Si:B. Here we will focus on the specific heat of two different superconducting samples of boron-doped SiC. One of them contains cubic and hexagonal SiC whereas the other consists mainly of hexagonal SiC without any detectable cubic phase fraction. The electronic specific heat in the superconducting state of both samples SiC:B can be described by either assuming a BCS-type exponentional temperature dependence or a power-law behavior. © 2009 IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
In 2004 the discovery of superconductivity in heavily boron-doped diamond (C:B) led to an increasing interest in the superconducting phases of wide-gap semiconductors. Subsequently superconductivity was found in heavily boron-doped cubic silicon (Si:B) and recently in the stochiometric "mixture" of heavily boron-doped silicon carbide (SiC:B). The latter system surprisingly exhibits type-I superconductivity in contrast to the type-II superconductors C:B and Si:B. Here we will focus on the specific heat of two different superconducting samples of boron-doped SiC. One of them contains cubic and hexagonal SiC whereas the other consists mainly of hexagonal SiC without any detectable cubic phase fraction. The electronic specific heat in the superconducting state of both samples SiC:B can be described by either assuming a BCS-type exponentional temperature dependence or a power-law behavior. © 2009 IOP Publishing Ltd.
633.
S Kittaka, T Nakamura, Y Aono, S Yonezawa, K Ishida, Y Maeno
Unusual temperature dependence of the in-plane critical field in Sr 2RuO4 Conference
vol. 150, no. 5, 2009.
@conference{Kittaka2009c,
title = {Unusual temperature dependence of the in-plane critical field in Sr 2RuO4},
author = {S Kittaka and T Nakamura and Y Aono and S Yonezawa and K Ishida and Y Maeno},
doi = {10.1088/1742-6596/150/5/052112},
year = {2009},
date = {2009-01-01},
journal = {Journal of Physics: Conference Series},
volume = {150},
number = {5},
abstract = {We have studied the upper critical field Hc2 of the spin-triplet superconductor Sr2RuO4. For H || c, Hc2 increases linearly with decreasing temperature down to well below Tc 1.5 K, consistent with the orbital depairing effect. However, for H || ab, the increase of Hc2 is strongly suppressed below 1 K. The origin of this in-plane Hc2 limit has been actively discussed, but its mechanism is still unclear. In the present study, we performed ac susceptibility measurements in the applied fields with higher accuracy than in previous studies to obtain the field-temperature phase diagrams for H || c and H || ab. We revealed that Hc2 || ab (T) does not exhibit a linear temperature dependence even above 1 K, which indicates that the Hc2 suppression is operative even close to Tc. In addition, we found that the Hc2 anisotropy ratio Hc2 || ab/Hc2 || c decreases monotonically from 60 to 20 with decreasing temperature. © 2009 IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
We have studied the upper critical field Hc2 of the spin-triplet superconductor Sr2RuO4. For H || c, Hc2 increases linearly with decreasing temperature down to well below Tc 1.5 K, consistent with the orbital depairing effect. However, for H || ab, the increase of Hc2 is strongly suppressed below 1 K. The origin of this in-plane Hc2 limit has been actively discussed, but its mechanism is still unclear. In the present study, we performed ac susceptibility measurements in the applied fields with higher accuracy than in previous studies to obtain the field-temperature phase diagrams for H || c and H || ab. We revealed that Hc2 || ab (T) does not exhibit a linear temperature dependence even above 1 K, which indicates that the Hc2 suppression is operative even close to Tc. In addition, we found that the Hc2 anisotropy ratio Hc2 || ab/Hc2 || c decreases monotonically from 60 to 20 with decreasing temperature. © 2009 IOP Publishing Ltd.
632.
S Yonezawa, S Kusaba, Y Maeno, P Auban-Senzier, C Pasquier, D Jérome
vol. 150, no. 5, 2009.
@conference{Yonezawa2009,
title = {Field-induced dimensional crossover and anomalous superconducting states in the quasi-one-dimensional superconductor (TMTSF)2C1O4},
author = {S Yonezawa and S Kusaba and Y Maeno and P Auban-Senzier and C Pasquier and D Jérome},
doi = {10.1088/1742-6596/150/5/052289},
year = {2009},
date = {2009-01-01},
journal = {Journal of Physics: Conference Series},
volume = {150},
number = {5},
abstract = {Quasi-one-dimensional (Q1D) superconductivity becomes stable in high magnetic fields due to the field-induced dimensional crossover (FIDO) and a stabilization of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states. We have studied the field-direction and field-amplitude dependence of the onset temperature Tonsetc of the superconducting state of the organic superconductor (TMTSF)2C1O4. Comparing the in-plane field-angle φ dependence of Tonsetc and the behavjor of the inter-plane resistance, we show that the FIDO stabilizes the superconductivity when the field is more than 19° away from the a axis. In addition, we demonstrate that Tonset remains finite for H || a up to H 50 kOe, as well as for H ∥ b. The high-field states are anomalous in nature, suggesting that different FFLO states are realized. © 2009 IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
Quasi-one-dimensional (Q1D) superconductivity becomes stable in high magnetic fields due to the field-induced dimensional crossover (FIDO) and a stabilization of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states. We have studied the field-direction and field-amplitude dependence of the onset temperature Tonsetc of the superconducting state of the organic superconductor (TMTSF)2C1O4. Comparing the in-plane field-angle φ dependence of Tonsetc and the behavjor of the inter-plane resistance, we show that the FIDO stabilizes the superconductivity when the field is more than 19° away from the a axis. In addition, we demonstrate that Tonset remains finite for H || a up to H 50 kOe, as well as for H ∥ b. The high-field states are anomalous in nature, suggesting that different FFLO states are realized. © 2009 IOP Publishing Ltd.
631.
H Nobukane, S Tsuchiya, K Konno, K Inagaki, S Tanda, I Kawasaki, H Amitsuka, K Tenya, Y Maeno
Magnetic rapid quench measurement in U(1) and SU(2) superconductors Conference
vol. 150, no. 5, 2009.
@conference{Nobukane2009,
title = {Magnetic rapid quench measurement in U(1) and SU(2) superconductors},
author = {H Nobukane and S Tsuchiya and K Konno and K Inagaki and S Tanda and I Kawasaki and H Amitsuka and K Tenya and Y Maeno},
doi = {10.1088/1742-6596/150/5/052187},
year = {2009},
date = {2009-01-01},
journal = {Journal of Physics: Conference Series},
volume = {150},
number = {5},
abstract = {We observed the power law and the critical exponent of quantum phase transitions by measuring a transient response in an Al/AlOx/Al junction of U(1) superconductors and Sr2RuO4 single crystals of SU(2) superconductors, when magnetic field decreased rapidly from more than the critical field to zero magnetic field below T 0.1 K. In the Al/AlOx/Al junction, the result shows that the domain length ξ is a power function of the quench time TQ. The critical exponent is 0.30 0.01. Moreover, in the Sr2RuO4 crystal, the result shows ξ is a power function of Tq and the critical exponent is 0.40 0.01. From the results of U(1) and SU(2) superconductors, we consider the critical exponents observed by the quenching are derived by a mean-field value in charged systems. Using typical U(1) and SU(2) superconductors, we find that the magnetic quench is efficient method to study formation processes of topological defects for a quantum phase transition near T 0. © 2009 IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
We observed the power law and the critical exponent of quantum phase transitions by measuring a transient response in an Al/AlOx/Al junction of U(1) superconductors and Sr2RuO4 single crystals of SU(2) superconductors, when magnetic field decreased rapidly from more than the critical field to zero magnetic field below T 0.1 K. In the Al/AlOx/Al junction, the result shows that the domain length ξ is a power function of the quench time TQ. The critical exponent is 0.30 0.01. Moreover, in the Sr2RuO4 crystal, the result shows ξ is a power function of Tq and the critical exponent is 0.40 0.01. From the results of U(1) and SU(2) superconductors, we consider the critical exponents observed by the quenching are derived by a mean-field value in charged systems. Using typical U(1) and SU(2) superconductors, we find that the magnetic quench is efficient method to study formation processes of topological defects for a quantum phase transition near T 0. © 2009 IOP Publishing Ltd.
630.
S Kittaka, S Yonezawa, H Yaguchi, Y Maeno, R Fittipaldi, A Vecchione, J -F Mercure, A Gibbs, R S Perry, A P MacKenzie
vol. 150, no. 5, 2009.
@conference{Kittaka2009d,
title = {Evidence for the Sr2RuO4 intercalations in the Sr3Ru2O7 region of the Sr3Ru 2O7 - Sr2RuO4 eutectic system},
author = {S Kittaka and S Yonezawa and H Yaguchi and Y Maeno and R Fittipaldi and A Vecchione and J -F Mercure and A Gibbs and R S Perry and A P MacKenzie},
doi = {10.1088/1742-6596/150/5/052113},
year = {2009},
date = {2009-01-01},
journal = {Journal of Physics: Conference Series},
volume = {150},
number = {5},
abstract = {Although Sr3Ru2O7 has not been reported to exhibit superconductivity so far, ac susceptibility measurements revealed multiple superconducting transitions occurring in the Sr3Ru 2O7 region cut from Sr3Ru2O 7 - Sr2RuO4 eutectic crystals. Based on various experimental results, some of us proposed the scenario in which Sr 2RuO4 thin slabs with a few layers of the RuO2 plane are embedded in the Sr3Ru2O7 region as stacking faults and multiple superconducting transitions arise from the distribution of the slab thickness. To examine this scenario, we measured the resistivity along the ab plane (ρab) using a Sr 3Ru2O7-region sample cut from the eutectic crystal, as well as along the c axis (ρc) using the same crystal. As a result, we detected resistance drops associated with superconductivity only in ρab, but not in ρc. These results support the Sr2RuO4 thin-slab scenario. In addition, we measured the resistivity of a single crystal of pure Sr3Ru2O 7with very high quality and found that pure Sr3Ru 2O7 does not exhibit superconductivity down to 15 mK. © 2009 IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
Although Sr3Ru2O7 has not been reported to exhibit superconductivity so far, ac susceptibility measurements revealed multiple superconducting transitions occurring in the Sr3Ru 2O7 region cut from Sr3Ru2O 7 - Sr2RuO4 eutectic crystals. Based on various experimental results, some of us proposed the scenario in which Sr 2RuO4 thin slabs with a few layers of the RuO2 plane are embedded in the Sr3Ru2O7 region as stacking faults and multiple superconducting transitions arise from the distribution of the slab thickness. To examine this scenario, we measured the resistivity along the ab plane (ρab) using a Sr 3Ru2O7-region sample cut from the eutectic crystal, as well as along the c axis (ρc) using the same crystal. As a result, we detected resistance drops associated with superconductivity only in ρab, but not in ρc. These results support the Sr2RuO4 thin-slab scenario. In addition, we measured the resistivity of a single crystal of pure Sr3Ru2O 7with very high quality and found that pure Sr3Ru 2O7 does not exhibit superconductivity down to 15 mK. © 2009 IOP Publishing Ltd.
629.
R Fittipaldi, M Cuoco, V Granata, C Noce, S Pace, D Stornaiuolo, D Born, F Tafuri, S Kittaka, Y Maeno, A Vecchione
Superconducting behaviour via percolation in Sr2RuO 4-Sr3Ru2O7 eutectic crystals Conference
vol. 150, no. 5, 2009.
@conference{Fittipaldi2009,
title = {Superconducting behaviour via percolation in Sr2RuO 4-Sr3Ru2O7 eutectic crystals},
author = {R Fittipaldi and M Cuoco and V Granata and C Noce and S Pace and D Stornaiuolo and D Born and F Tafuri and S Kittaka and Y Maeno and A Vecchione},
doi = {10.1088/1742-6596/150/5/052056},
year = {2009},
date = {2009-01-01},
journal = {Journal of Physics: Conference Series},
volume = {150},
number = {5},
abstract = {We report on superconducting behavior of Sr3Ru2O 7 macrodomain taken out from Sr2RuO4-Sr 3Ru2O7 eutectic crystals. Transport measurements performed down to 300 mK provide evidence of a supercurrent flowing through the whole sample. Structural and compositional analyses are used to estimate the percentage of possible Sr2RuO4 inclusions. On the base of a model that describes the system as a proximity network made of superconducting Sr2RuO4 grains dispersed in the normal Sr3Ru2O7 matrix we determine the conditions for having a percolating superflow through the system. © 2009 IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
We report on superconducting behavior of Sr3Ru2O 7 macrodomain taken out from Sr2RuO4-Sr 3Ru2O7 eutectic crystals. Transport measurements performed down to 300 mK provide evidence of a supercurrent flowing through the whole sample. Structural and compositional analyses are used to estimate the percentage of possible Sr2RuO4 inclusions. On the base of a model that describes the system as a proximity network made of superconducting Sr2RuO4 grains dispersed in the normal Sr3Ru2O7 matrix we determine the conditions for having a percolating superflow through the system. © 2009 IOP Publishing Ltd.
628.
K Ishida, Y Nakai, S Kitagawa, Y Kamihara, M Hirano, H Hosono
75As and 139La NMR studies on LaFeAs (O1 - x Fx) Journal Article
In: Physica B: Condensed Matter, vol. 404, no. 19, pp. 3089-3094, 2009.
@article{Ishida20093089,
title = {75As and 139La NMR studies on LaFeAs (O1 - x Fx)},
author = {K Ishida and Y Nakai and S Kitagawa and Y Kamihara and M Hirano and H Hosono},
doi = {10.1016/j.physb.2009.07.078},
year = {2009},
date = {2009-01-01},
journal = {Physica B: Condensed Matter},
volume = {404},
number = {19},
pages = {3089-3094},
abstract = {We report experimental results of 75As and 139La nuclear magnetic resonance (NMR) in the layered oxypnictide system LaFeAs (O1 - x Fx) (x = 0.0, 0.04, 0.07 and 0.11) where superconductivity occurs in x greater than 0.04. In the undoped LaFeAsO, 1 / T1 of 139La exhibits a distinct peak at TN ~ 142 K below which the La NMR spectra become broadened due to the internal magnetic field attributed to an antiferromagnetic (AFM) ordering. In the x = 0.04 sample, 1 / T1 T of 75As exhibits a Curie-Weiss temperature dependence down to 30 K, suggesting the development of AFM spin fluctuations with decreasing temperature. In the x = 0.11 sample, in contrast, pseudogap behavior is observed in 1 / T1 T at the 75As site with a gap value of ΔPG ~ 175 K. The spin dynamics vary markedly with F-doping, which is ascribed to the change of the Fermi-surface structure by the electron-doping. As for the superconducting properties for x = 0.04, 0.07 and 0.11, 1 / T1 of 75As in all compounds does not exhibit a coherence peak just below Tc and follows a T3 dependence at low temperatures. These results seemingly suggests that unconventional superconductivity with zero gap along lines, whereas the lack of the residual density of states at the low temperatures is incompatible with the presence of the line-nodes. We discuss similarity and difference between LaFeAs (O1 - x Fx) and cuprates, and also discuss the relationship between spin dynamics and superconductivity on the basis of F-doping dependence of Tc and 1 / T1. Crown Copyright © 2009.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report experimental results of 75As and 139La nuclear magnetic resonance (NMR) in the layered oxypnictide system LaFeAs (O1 - x Fx) (x = 0.0, 0.04, 0.07 and 0.11) where superconductivity occurs in x greater than 0.04. In the undoped LaFeAsO, 1 / T1 of 139La exhibits a distinct peak at TN ~ 142 K below which the La NMR spectra become broadened due to the internal magnetic field attributed to an antiferromagnetic (AFM) ordering. In the x = 0.04 sample, 1 / T1 T of 75As exhibits a Curie-Weiss temperature dependence down to 30 K, suggesting the development of AFM spin fluctuations with decreasing temperature. In the x = 0.11 sample, in contrast, pseudogap behavior is observed in 1 / T1 T at the 75As site with a gap value of ΔPG ~ 175 K. The spin dynamics vary markedly with F-doping, which is ascribed to the change of the Fermi-surface structure by the electron-doping. As for the superconducting properties for x = 0.04, 0.07 and 0.11, 1 / T1 of 75As in all compounds does not exhibit a coherence peak just below Tc and follows a T3 dependence at low temperatures. These results seemingly suggests that unconventional superconductivity with zero gap along lines, whereas the lack of the residual density of states at the low temperatures is incompatible with the presence of the line-nodes. We discuss similarity and difference between LaFeAs (O1 - x Fx) and cuprates, and also discuss the relationship between spin dynamics and superconductivity on the basis of F-doping dependence of Tc and 1 / T1. Crown Copyright © 2009.
627.
Y Nambu, R T MacAluso, T Higo, K Ishida, S Nakatsuji
Structural properties of the two-dimensional triangular antiferromagnet NiGa2 S4 Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 79, no. 21, 2009.
@article{Nambu2009,
title = {Structural properties of the two-dimensional triangular antiferromagnet NiGa2 S4},
author = {Y Nambu and R T MacAluso and T Higo and K Ishida and S Nakatsuji},
doi = {10.1103/PhysRevB.79.214108},
year = {2009},
date = {2009-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {79},
number = {21},
abstract = {Polycrystalline samples of NiGa2 S4+δ (-0.2≤δ≤+0.2) have been synthesized by solid-state reaction. X-ray powder-diffraction measurements indicate that these samples are single phase with a trigonal lattice with a nominal concentration δ at least between -0.12 and +0.16. Rietveld analyses for time-of-flight neutron-diffraction data have revealed that there is no site mixing between Ni and Ga atoms, indicating that the triangular lattice is only formed by Ni atoms. Our susceptibility measurements have clarified that the freezing temperature and the magnitude of hysteresis systematically change with nominal sulfur concentration and form a respective peak and minimum at the nominal NiGa2 S4.04. These results together with our chemical analyses indicate that the actual content of sulfur for the nominal NiGa2 S4.04 should be stoichiometric, namely, 4.00. On the contrary, the Ga nuclear quadrupole resonance (NQR) has suggested the presence of two different Ga sites from the Ga-NQR spectra in both samples with the nominal concentration of NiGa2 S4.00 and NiGa2 S4.04, despite the fact that there is a single crystallographic site for Ga in the unit cell. High-resolution transmission electron microscopy scans conducted over a wide region of a NiGa2 S4.04 single crystal found a clean defect-free in-plane structure. Diffraction patterns of the selected area indicate the partial presence of a superlatticelike stacking fault. This suggests that the two different Ga sites are not generated by the sulfur deficiency but by the superlatticelike stacking fault. © 2009 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Polycrystalline samples of NiGa2 S4+δ (-0.2≤δ≤+0.2) have been synthesized by solid-state reaction. X-ray powder-diffraction measurements indicate that these samples are single phase with a trigonal lattice with a nominal concentration δ at least between -0.12 and +0.16. Rietveld analyses for time-of-flight neutron-diffraction data have revealed that there is no site mixing between Ni and Ga atoms, indicating that the triangular lattice is only formed by Ni atoms. Our susceptibility measurements have clarified that the freezing temperature and the magnitude of hysteresis systematically change with nominal sulfur concentration and form a respective peak and minimum at the nominal NiGa2 S4.04. These results together with our chemical analyses indicate that the actual content of sulfur for the nominal NiGa2 S4.04 should be stoichiometric, namely, 4.00. On the contrary, the Ga nuclear quadrupole resonance (NQR) has suggested the presence of two different Ga sites from the Ga-NQR spectra in both samples with the nominal concentration of NiGa2 S4.00 and NiGa2 S4.04, despite the fact that there is a single crystallographic site for Ga in the unit cell. High-resolution transmission electron microscopy scans conducted over a wide region of a NiGa2 S4.04 single crystal found a clean defect-free in-plane structure. Diffraction patterns of the selected area indicate the partial presence of a superlatticelike stacking fault. This suggests that the two different Ga sites are not generated by the sulfur deficiency but by the superlatticelike stacking fault. © 2009 The American Physical Society.
626.
Y Nakai, S Kitagawa, K Ishida, Y Kamihara, M Hirano, H Hosono
Systematic A 75 s NMR study of the dependence of low-lying excitations on F doping in the iron oxypnictide LaFeAsO1-x Fx Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 79, no. 21, 2009.
@article{Nakai2009,
title = {Systematic A 75 s NMR study of the dependence of low-lying excitations on F doping in the iron oxypnictide LaFeAsO1-x Fx},
author = {Y Nakai and S Kitagawa and K Ishida and Y Kamihara and M Hirano and H Hosono},
doi = {10.1103/PhysRevB.79.212506},
year = {2009},
date = {2009-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {79},
number = {21},
abstract = {We report A 75 s NMR studies on LaFeAs (O1-x Fx) (0≤x≤0.14). At x=0.04 near the phase boundary, from resistivity, spin-lattice relaxation rate 1/ T1, and NMR spectrum measurements, we found weak magnetic order at TN □30 K. Antiferromagnetic (AFM) fluctuations proved through 1/ T1 are suppressed significantly with F doping, and pseudogap behavior without pronounced AFM fluctuations is observed at x=0.11 where TC is maximum. This significant suppression of 1/ T1 T upon F doping while TC remains nearly unchanged suggests that low-energy AFM fluctuations probed with A 75 s NMR do not play a crucial role in the superconductivity. © 2009 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report A 75 s NMR studies on LaFeAs (O1-x Fx) (0≤x≤0.14). At x=0.04 near the phase boundary, from resistivity, spin-lattice relaxation rate 1/ T1, and NMR spectrum measurements, we found weak magnetic order at TN □30 K. Antiferromagnetic (AFM) fluctuations proved through 1/ T1 are suppressed significantly with F doping, and pseudogap behavior without pronounced AFM fluctuations is observed at x=0.11 where TC is maximum. This significant suppression of 1/ T1 T upon F doping while TC remains nearly unchanged suggests that low-energy AFM fluctuations probed with A 75 s NMR do not play a crucial role in the superconductivity. © 2009 The American Physical Society.
625.
K Ishida, Y Nakai, H Hosono
To what extent iron-pnictide new superconductors have been clarified: A progress report Journal Article
In: Journal of the Physical Society of Japan, vol. 78, no. 6, 2009.
@article{Ishida2009b,
title = {To what extent iron-pnictide new superconductors have been clarified: A progress report},
author = {K Ishida and Y Nakai and H Hosono},
doi = {10.1143/JPSJ.78.062001},
year = {2009},
date = {2009-01-01},
journal = {Journal of the Physical Society of Japan},
volume = {78},
number = {6},
abstract = {In this review, the authors present a summary of experimental reports on newly discovered iron-based superconductors as they were known at the end of 2008. At the same time, this paper is intended to be useful for experimenters to know the current status of these superconductors. The authors introduce experimental results that reveal basic physical properties in the normal and superconducting states. The similarities and differences between iron-pnictide superconductors and other unconventional superconductors are also discussed. © 2009 The Physical Society of Japan.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In this review, the authors present a summary of experimental reports on newly discovered iron-based superconductors as they were known at the end of 2008. At the same time, this paper is intended to be useful for experimenters to know the current status of these superconductors. The authors introduce experimental results that reveal basic physical properties in the normal and superconducting states. The similarities and differences between iron-pnictide superconductors and other unconventional superconductors are also discussed. © 2009 The Physical Society of Japan.
624.
Y Nakai, S Kitagawa, K Ishida, Y Kamihara, M Hirano, H Hosono
An NMR study on the F-doping evolution of the iron oxypnictide LaFeAs(O1-xFx) Journal Article
In: New Journal of Physics, vol. 11, 2009.
@article{Nakai2009b,
title = {An NMR study on the F-doping evolution of the iron oxypnictide LaFeAs(O1-xFx)},
author = {Y Nakai and S Kitagawa and K Ishida and Y Kamihara and M Hirano and H Hosono},
doi = {10.1088/1367-2630/11/4/045004},
year = {2009},
date = {2009-01-01},
journal = {New Journal of Physics},
volume = {11},
abstract = {We report the experimental results of 75As and 139La nuclear magnetic resonance (NMR) in the layered oxypnictide system LaFeAs(O 1−xFx) (x = 0.0, 0.04, 0.07, 0.11 and 0.14) where superconductivity occurs at x > 0.03. In the undoped LaFeAsO, 1/T 1 of 139La exhibits a distinct peak at TiN ∼ 142 K below which the La-NMR spectra become broadened due to the internal magnetic field attributed to an antiferromagnetic (AFM) ordering. In the x = 0.04 sample, 1/T1T of 75As exhibits a Curie-Weiss temperature dependence down to 30 K, suggesting the development of AFM spin fluctuations with a decrease in temperature. At x = 0.11 and 0.14, in contrast, pseudogap behavior is observed in 1/ T1T at the 75As site with a gap value of δPG ∼ 175 and 165 K, respectively. The spin dynamics vary markedly with F-doping, which is ascribed to the change of the Fermi-surface structure because of the electron doping. As for the superconducting properties for x = 0.04, 0.07 and 0.11, the 1 / T1 of75 As in the three samples does not exhibit a coherence peak just below Tc and follows a T3 dependence at low temperatures. These results may suggest unconventional superconductivity with a zero gap along the lines, but neither the field-induced extra relaxation rate nor the residual density of states at the low temperatures is incompatible with the presence of the line nodes. We discuss the similarities and differences between LaFeAs(O1−xFx) and cuprates and also discuss the relationship between spin dynamics and superconductivity on the basis of the F-doping dependence of Tc and 1/T1. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report the experimental results of 75As and 139La nuclear magnetic resonance (NMR) in the layered oxypnictide system LaFeAs(O 1&#8722;xFx) (x = 0.0, 0.04, 0.07, 0.11 and 0.14) where superconductivity occurs at x > 0.03. In the undoped LaFeAsO, 1/T 1 of 139La exhibits a distinct peak at TiN ∼ 142 K below which the La-NMR spectra become broadened due to the internal magnetic field attributed to an antiferromagnetic (AFM) ordering. In the x = 0.04 sample, 1/T1T of 75As exhibits a Curie-Weiss temperature dependence down to 30 K, suggesting the development of AFM spin fluctuations with a decrease in temperature. At x = 0.11 and 0.14, in contrast, pseudogap behavior is observed in 1/ T1T at the 75As site with a gap value of δPG ∼ 175 and 165 K, respectively. The spin dynamics vary markedly with F-doping, which is ascribed to the change of the Fermi-surface structure because of the electron doping. As for the superconducting properties for x = 0.04, 0.07 and 0.11, the 1 / T1 of75 As in the three samples does not exhibit a coherence peak just below Tc and follows a T3 dependence at low temperatures. These results may suggest unconventional superconductivity with a zero gap along the lines, but neither the &#64257;eld-induced extra relaxation rate nor the residual density of states at the low temperatures is incompatible with the presence of the line nodes. We discuss the similarities and differences between LaFeAs(O1&#8722;xFx) and cuprates and also discuss the relationship between spin dynamics and superconductivity on the basis of the F-doping dependence of Tc and 1/T1. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
623.
D E MacLaughlin, Y Ohta, Y Machida, S Nakatsuji, G M Luke, K Ishida, R H Heffner, L Shu, O O Bernal
Weak quasistatic magnetism in the frustrated Kondo lattice Pr2Ir2O7 Journal Article
In: Physica B: Condensed Matter, vol. 404, no. 5-7, pp. 667-670, 2009.
@article{MacLaughlin2009667,
title = {Weak quasistatic magnetism in the frustrated Kondo lattice Pr2Ir2O7},
author = {D E MacLaughlin and Y Ohta and Y Machida and S Nakatsuji and G M Luke and K Ishida and R H Heffner and L Shu and O O Bernal},
doi = {10.1016/j.physb.2008.11.167},
year = {2009},
date = {2009-01-01},
journal = {Physica B: Condensed Matter},
volume = {404},
number = {5-7},
pages = {667-670},
abstract = {Muon spin relaxation experiments have been performed in the pyrochlore iridate Pr2Ir2O7 for temperatures in the range 0.025-250 K. Kubo-Toyabe relaxation functions are observed up to ≳ 200 K, indicating static magnetism over this temperature range. The T → 0 static muon spin relaxation rate Δ (0) ≈ 8 μ s- 1 implies a weak quasistatic moment (∼ 0.1 μB). The temperature dependence of Δ is highly nonmean-field-like, decreasing smoothly by orders of magnitude but remaining nonzero for T < Tf. The data rule out ordering of the full Pr3 + CEF ground-state moment (3.0 μB) down to 0.025 K. The weak static magnetism is most likely due to hyperfine-enhanced 141Pr nuclear magnetism. The dynamic relaxation rate λ increases markedly below ∼ 20 K, probably due to slowing down of spin fluctuations in the spin-liquid state. At low temperatures λ is strong and temperature-independent, indicative of a high density of low-lying spin excitations as is common in frustrated antiferromagnets. © 2008 Elsevier B.V.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Muon spin relaxation experiments have been performed in the pyrochlore iridate Pr2Ir2O7 for temperatures in the range 0.025-250 K. Kubo-Toyabe relaxation functions are observed up to ≳ 200 K, indicating static magnetism over this temperature range. The T → 0 static muon spin relaxation rate Δ (0) ≈ 8 μ s- 1 implies a weak quasistatic moment (∼ 0.1 μB). The temperature dependence of Δ is highly nonmean-field-like, decreasing smoothly by orders of magnitude but remaining nonzero for T < Tf. The data rule out ordering of the full Pr3 + CEF ground-state moment (3.0 μB) down to 0.025 K. The weak static magnetism is most likely due to hyperfine-enhanced 141Pr nuclear magnetism. The dynamic relaxation rate λ increases markedly below ∼ 20 K, probably due to slowing down of spin fluctuations in the spin-liquid state. At low temperatures λ is strong and temperature-independent, indicative of a high density of low-lying spin excitations as is common in frustrated antiferromagnets. © 2008 Elsevier B.V.
622.
Y Ihara, H Takeya, K Ishida, K Yoshimura, K Takada, T Sasaki, H Sakurai, E Takayama-Muromachi
Magnetic anomalies of hydrous cobaltate compound Nax(H 3O)zCoO2·yH2O detected by NMR and NQR measurements Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 79, no. 2, 2009.
@article{Ihara2009,
title = {Magnetic anomalies of hydrous cobaltate compound Nax(H 3O)zCoO2·yH2O detected by NMR and NQR measurements},
author = {Y Ihara and H Takeya and K Ishida and K Yoshimura and K Takada and T Sasaki and H Sakurai and E Takayama-Muromachi},
doi = {10.1103/PhysRevB.79.024510},
year = {2009},
date = {2009-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {79},
number = {2},
abstract = {In order to investigate the relationship between superconductivity and magnetism in bilayer-hydrate cobaltate Nax (H3 O) z CoO2·y H2 O Co nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements were performed on three different samples, which demonstrate various ground states at low temperatures. The appearance of small internal fields is observed in the NQR spectra below approximately 6 K on one of the samples that possesses the largest c -axis length and the highest NQR frequency. The other two samples exhibit superconducting transition in zero magnetic field, while these two samples show different ground states in the magnetic fields greater than 5 T. The comparison of the NMR spectra of these two samples obtained in high magnetic fields reveals the appearance of static internal magnetic fields at the Co site below 4 K in the sample that possesses the intermediate c -axis length and the NQR frequency. © 2009 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In order to investigate the relationship between superconductivity and magnetism in bilayer-hydrate cobaltate Nax (H3 O) z CoO2·y H2 O Co nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements were performed on three different samples, which demonstrate various ground states at low temperatures. The appearance of small internal fields is observed in the NQR spectra below approximately 6 K on one of the samples that possesses the largest c -axis length and the highest NQR frequency. The other two samples exhibit superconducting transition in zero magnetic field, while these two samples show different ground states in the magnetic fields greater than 5 T. The comparison of the NMR spectra of these two samples obtained in high magnetic fields reveals the appearance of static internal magnetic fields at the Co site below 4 K in the sample that possesses the intermediate c -axis length and the NQR frequency. © 2009 The American Physical Society.
621.
Y Nakai, S Kitagawa, K Ishida, Y Kamihara, M Hirano, H Hosono
75As and 139La NMR/NQR investigations of iron-based superconductor LaFeAs(O0.89F0.11) Conference
vol. 150, no. 5, 2009.
@conference{Nakai2009c,
title = {75As and 139La NMR/NQR investigations of iron-based superconductor LaFeAs(O0.89F0.11)},
author = {Y Nakai and S Kitagawa and K Ishida and Y Kamihara and M Hirano and H Hosono},
doi = {10.1088/1742-6596/150/5/052179},
year = {2009},
date = {2009-01-01},
journal = {Journal of Physics: Conference Series},
volume = {150},
number = {5},
abstract = {We report 75As and 139La NMR/NQR results in LaFeAs(O0.89F0.11). In the normal state, 1/T1T decreases with lowered temperature, which is reminiscent of the pseudogap behavior in the high-Tc cuprates. In the superconducting (SC) state, 1/T1 decreases suddenly below Tc without a Hebel-Slichter coherence peak, followed by a T3 dependence, which is characteristics of unconventional superconductors with lines of nodes. However, the residual density of states in the low temperatures, which is usually observed in unconventional superconductors with crystal imperfections and/or impurity phases, was not observed. Knight shift measurements show that spin susceptibility decreases in the SC state. © 2009 IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
We report 75As and 139La NMR/NQR results in LaFeAs(O0.89F0.11). In the normal state, 1/T1T decreases with lowered temperature, which is reminiscent of the pseudogap behavior in the high-Tc cuprates. In the superconducting (SC) state, 1/T1 decreases suddenly below Tc without a Hebel-Slichter coherence peak, followed by a T3 dependence, which is characteristics of unconventional superconductors with lines of nodes. However, the residual density of states in the low temperatures, which is usually observed in unconventional superconductors with crystal imperfections and/or impurity phases, was not observed. Knight shift measurements show that spin susceptibility decreases in the SC state. © 2009 IOP Publishing Ltd.
620.
D E MacLaughlin, S Nakatsuji, Y Nambu, K Ishida, R H Heffner, L Shu, O O Bernal
Unconventional spin freezing and fluctuations in the frustrated antiferromagnet NiGa2S4 Conference
vol. 145, no. 1, 2009.
@conference{MacLaughlin2009b,
title = {Unconventional spin freezing and fluctuations in the frustrated antiferromagnet NiGa2S4},
author = {D E MacLaughlin and S Nakatsuji and Y Nambu and K Ishida and R H Heffner and L Shu and O O Bernal},
doi = {10.1088/1742-6596/145/1/012040},
year = {2009},
date = {2009-01-01},
journal = {Journal of Physics: Conference Series},
volume = {145},
number = {1},
abstract = {Longitudinal-field muon spin rotation (LF-μSR) experiments in the two- dimensional geometrically-frustrated antiferromagnet NiGa2S4 reveal a number of features of spin freezing and dynamics in this system. Long-lived (correlation time 10-6 s at 2 K) disordered Ni spin freezing sets in abruptly below Tf = 8:5±0:5 K. At low temperatures slow Ni spin fluctuations are found in low applied field HL that are rapidly suppressed for HL and 0:04 T. Activated muon spin relaxation above Tf is strong evidence for 2D critical behaviour. The LF-μSR data indicate that NiGa2S4 is neither a conventional magnet nor a singlet spin liquid, and raise the question of how to reconcile the strongly field-dependent muon relaxation with the field-independent specific heat. © 2009 IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
Longitudinal-field muon spin rotation (LF-μSR) experiments in the two- dimensional geometrically-frustrated antiferromagnet NiGa2S4 reveal a number of features of spin freezing and dynamics in this system. Long-lived (correlation time 10-6 s at 2 K) disordered Ni spin freezing sets in abruptly below Tf = 8:5±0:5 K. At low temperatures slow Ni spin fluctuations are found in low applied field HL that are rapidly suppressed for HL and 0:04 T. Activated muon spin relaxation above Tf is strong evidence for 2D critical behaviour. The LF-μSR data indicate that NiGa2S4 is neither a conventional magnet nor a singlet spin liquid, and raise the question of how to reconcile the strongly field-dependent muon relaxation with the field-independent specific heat. © 2009 IOP Publishing Ltd.
2008
619.
H Kambara, S Kashiwaya, H Yaguchi, Y Asano, Y Tanaka, Y Maeno
Anomalous transport through the p-wave superconducting channel in the 3-K phase of Sr2RuO4 Journal Article
In: Physical Review Letters, vol. 101, no. 26, 2008.
@article{Kambara2008,
title = {Anomalous transport through the p-wave superconducting channel in the 3-K phase of Sr2RuO4},
author = {H Kambara and S Kashiwaya and H Yaguchi and Y Asano and Y Tanaka and Y Maeno},
doi = {10.1103/PhysRevLett.101.267003},
year = {2008},
date = {2008-01-01},
journal = {Physical Review Letters},
volume = {101},
number = {26},
abstract = {Using microfabrication techniques, we extracted individual channels of 3-kelvin (3-K) phase superconductivity in Sr2RuO4-Ru eutectic systems and confirmed odd-parity superconductivity in the 3-K phase, similar to pure Sr2RuO4. Unusual hysteresis in the differential resistance-current and voltage-current characteristics observed below 2 K indicates the internal degrees of freedom of the superconducting state. A possible origin of the hysteresis is current-induced chiral-domain-wall motion due to the chiral p-wave state. © 2008 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Using microfabrication techniques, we extracted individual channels of 3-kelvin (3-K) phase superconductivity in Sr2RuO4-Ru eutectic systems and confirmed odd-parity superconductivity in the 3-K phase, similar to pure Sr2RuO4. Unusual hysteresis in the differential resistance-current and voltage-current characteristics observed below 2 K indicates the internal degrees of freedom of the superconducting state. A possible origin of the hysteresis is current-induced chiral-domain-wall motion due to the chiral p-wave state. © 2008 The American Physical Society.
618.
K Ishida, H Murakawa, H Mukuda, Y Kitaoka, Z Q Mao, Y Maeno
NMR and NQR studies on superconducting Sr2RuO4 Journal Article
In: Journal of Physics and Chemistry of Solids, vol. 69, no. 12, pp. 3108-3114, 2008.
@article{Ishida20083108,
title = {NMR and NQR studies on superconducting Sr2RuO4},
author = {K Ishida and H Murakawa and H Mukuda and Y Kitaoka and Z Q Mao and Y Maeno},
doi = {10.1016/j.jpcs.2008.06.028},
year = {2008},
date = {2008-01-01},
journal = {Journal of Physics and Chemistry of Solids},
volume = {69},
number = {12},
pages = {3108-3114},
abstract = {We review our nuclear-magnetic resonance (NMR) and nuclear-quadrupole-resonance (NQR) studies in superconducting Sr2RuO4, which have been performed in order to investigate the gap structure and the pairing symmetry in the superconducting state and magnetic fluctuations in the normal state. The spin-lattice relaxation rate (1 / T1) of a high-quality sample with Tc ∼ 1.5 K shows a sharp decrease without a coherence peak just below Tc, followed by a T3 behavior down to 0.15 K. This result indicates that the superconducting gap in pure Sr2RuO4 is a highly anisotropic character with a line-node gap. The Knight shift, which is related to the spin susceptibility, is unchanged in the superconducting state irrespective of the direction of the applied fields and various magnitude of the field. This result strongly suggests that the superconducting pairs are in the spin-triplet state, and the spin direction of the triplet pairs is considered to be changed by small fields of several hundred Oe. © 2008 Elsevier Ltd. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We review our nuclear-magnetic resonance (NMR) and nuclear-quadrupole-resonance (NQR) studies in superconducting Sr2RuO4, which have been performed in order to investigate the gap structure and the pairing symmetry in the superconducting state and magnetic fluctuations in the normal state. The spin-lattice relaxation rate (1 / T1) of a high-quality sample with Tc ∼ 1.5 K shows a sharp decrease without a coherence peak just below Tc, followed by a T3 behavior down to 0.15 K. This result indicates that the superconducting gap in pure Sr2RuO4 is a highly anisotropic character with a line-node gap. The Knight shift, which is related to the spin susceptibility, is unchanged in the superconducting state irrespective of the direction of the applied fields and various magnitude of the field. This result strongly suggests that the superconducting pairs are in the spin-triplet state, and the spin direction of the triplet pairs is considered to be changed by small fields of several hundred Oe. © 2008 Elsevier Ltd. All rights reserved.
617.
S Kusaba, S Yonezawa, Y Maeno, P Auban-Senzier, C Pasquier, K Bechgaard, D Jérome
Precise determination of the in-plane superconducting anisotropy of (TMTSF)2ClO4 Journal Article
In: Solid State Sciences, vol. 10, no. 12, pp. 1768-1772, 2008.
@article{Kusaba20081768,
title = {Precise determination of the in-plane superconducting anisotropy of (TMTSF)2ClO4},
author = {S Kusaba and S Yonezawa and Y Maeno and P Auban-Senzier and C Pasquier and K Bechgaard and D Jérome},
doi = {10.1016/j.solidstatesciences.2008.04.011},
year = {2008},
date = {2008-01-01},
journal = {Solid State Sciences},
volume = {10},
number = {12},
pages = {1768-1772},
abstract = {We report the in-plane anisotropy of the onset of superconductivity in the organic superconductor (TMTSF)2ClO4 in magnetic fields H accurately aligned to the most conductive ab′ plane. We revealed that the rapid increase of the onset fields at low temperatures occurs for both H∥a and H∥b′, in spite of the change in dimensionality of the electronic system due to the field-induced dimensional crossover. However, the overall behavior of the curves is qualitatively different, indicating that the superconducting states realized for H∥a and H∥b′ have different natures. Moreover, we observed that the rapid increase of the onset fields for H∥a is rather sensitive to the rotation of the magnetic field within the ab′ plane than that for H∥b′. This different dependence on the rotation of the magnetic field within the ab′ plane suggests that the suppression of the interlayer hopping plays an important role to realize the different superconducting natures for H∥a and H∥b′. © 2008 Elsevier Masson SAS. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report the in-plane anisotropy of the onset of superconductivity in the organic superconductor (TMTSF)2ClO4 in magnetic fields H accurately aligned to the most conductive ab′ plane. We revealed that the rapid increase of the onset fields at low temperatures occurs for both H∥a and H∥b′, in spite of the change in dimensionality of the electronic system due to the field-induced dimensional crossover. However, the overall behavior of the curves is qualitatively different, indicating that the superconducting states realized for H∥a and H∥b′ have different natures. Moreover, we observed that the rapid increase of the onset fields for H∥a is rather sensitive to the rotation of the magnetic field within the ab′ plane than that for H∥b′. This different dependence on the rotation of the magnetic field within the ab′ plane suggests that the suppression of the interlayer hopping plays an important role to realize the different superconducting natures for H∥a and H∥b′. © 2008 Elsevier Masson SAS. All rights reserved.
616.
Y Pennec, N J C Ingle, I S Elfimov, E Varene, Y Maeno, A Damascelli, J V Barth
Cleaving-temperature dependence of layered-oxide surfaces Journal Article
In: Physical Review Letters, vol. 101, no. 21, 2008.
@article{Pennec2008,
title = {Cleaving-temperature dependence of layered-oxide surfaces},
author = {Y Pennec and N J C Ingle and I S Elfimov and E Varene and Y Maeno and A Damascelli and J V Barth},
doi = {10.1103/PhysRevLett.101.216103},
year = {2008},
date = {2008-01-01},
journal = {Physical Review Letters},
volume = {101},
number = {21},
abstract = {The surfaces generated by cleaving nonpolar, two-dimensional oxides are often considered to be perfect or ideal. However, single particle spectroscopies on Sr2RuO4, an archetypal nonpolar two-dimensional oxide, show significant cleavage temperature dependence. We demonstrate that this is not a consequence of the intrinsic characteristics of the surface: lattice parameters and symmetries, step heights, atom positions, or density of states. Instead, we find a marked increase in the density of defects at the mesoscopic scale with increased cleave temperature. The potential generality of these defects to oxide surfaces may have broad consequences to interfacial control and the interpretation of surface sensitive measurements. © 2008 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The surfaces generated by cleaving nonpolar, two-dimensional oxides are often considered to be perfect or ideal. However, single particle spectroscopies on Sr2RuO4, an archetypal nonpolar two-dimensional oxide, show significant cleavage temperature dependence. We demonstrate that this is not a consequence of the intrinsic characteristics of the surface: lattice parameters and symmetries, step heights, atom positions, or density of states. Instead, we find a marked increase in the density of defects at the mesoscopic scale with increased cleave temperature. The potential generality of these defects to oxide surfaces may have broad consequences to interfacial control and the interpretation of surface sensitive measurements. © 2008 The American Physical Society.
615.
Y Nambu, S Nakatsuji, Y Maeno, E K Okudzeto, J Y Chan
Spin dependent impurity effects on the 2D frustrated magnetism of NiGa2S4 Journal Article
In: Physical Review Letters, vol. 101, no. 20, 2008.
@article{Nambu2008,
title = {Spin dependent impurity effects on the 2D frustrated magnetism of NiGa2S4},
author = {Y Nambu and S Nakatsuji and Y Maeno and E K Okudzeto and J Y Chan},
doi = {10.1103/PhysRevLett.101.207204},
year = {2008},
date = {2008-01-01},
journal = {Physical Review Letters},
volume = {101},
number = {20},
abstract = {Impurity effects on the triangular antiferromagnets Ni1-xMxGa2S4 (M=Mn, Fe, Co and Zn) are studied. The 2D frozen spin-disordered state of NiGa2S4 is stable against the substitution of Zn2+ (S=0) and Heisenberg Fe2+ (S=2) spins, and exhibits a T2-dependent magnetic specific heat, scaled by the Weiss temperature. In contrast, the substitutions with Co2+ (S=3/2) spin with Ising-like anisotropy and Heisenberg Mn2+ (S=5/2) spin induce a conventional spin glass phase below 1 K. From these comparisons, it is suggested that the integer size of the Heisenberg spins is important to stabilize the 2D coherent behavior observed in the frozen spin-disordered state. © 2008 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Impurity effects on the triangular antiferromagnets Ni1-xMxGa2S4 (M=Mn, Fe, Co and Zn) are studied. The 2D frozen spin-disordered state of NiGa2S4 is stable against the substitution of Zn2+ (S=0) and Heisenberg Fe2+ (S=2) spins, and exhibits a T2-dependent magnetic specific heat, scaled by the Weiss temperature. In contrast, the substitutions with Co2+ (S=3/2) spin with Ising-like anisotropy and Heisenberg Mn2+ (S=5/2) spin induce a conventional spin glass phase below 1 K. From these comparisons, it is suggested that the integer size of the Heisenberg spins is important to stabilize the 2D coherent behavior observed in the frozen spin-disordered state. © 2008 The American Physical Society.
614.
H Yamaguchi, S Kimura, M Hagiwara, Y Nambu, S Nakatsuji, Y Maeno, K Kindo
High-field electron spin resonance in the two-dimensional triangular-lattice antiferromagnet NiGa2S4 Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 78, no. 18, 2008.
@article{Yamaguchi2008,
title = {High-field electron spin resonance in the two-dimensional triangular-lattice antiferromagnet NiGa2S4},
author = {H Yamaguchi and S Kimura and M Hagiwara and Y Nambu and S Nakatsuji and Y Maeno and K Kindo},
doi = {10.1103/PhysRevB.78.180404},
year = {2008},
date = {2008-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {78},
number = {18},
abstract = {We report experimental results of high-field electron spin resonance (ESR) measurements in magnetic fields up to about 53 T on the quasi-two-dimensional triangular-lattice antiferromagnet NiGa2 S4. From the temperature evolution of the ESR absorption linewidth, we find three distinct temperature regions: those (i) above 23 K, (ii) between 23 K and 8.5 K, and (iii) below 8.5 K. The linewidth is affected by the dynamics of Z2 vortices below 23 K and one of the conventional spiral resonance modes explains well the frequency dependence of the ESR resonance fields far below 8.5 K. Furthermore, we found an anomaly in the magnetization curve around one third of the saturation magnetization for H⊥c, corresponding to softening of another resonance mode. These results suggest the occurrence of a Z2 vortex-induced topological transition at 8.5 K. © 2008 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report experimental results of high-field electron spin resonance (ESR) measurements in magnetic fields up to about 53 T on the quasi-two-dimensional triangular-lattice antiferromagnet NiGa2 S4. From the temperature evolution of the ESR absorption linewidth, we find three distinct temperature regions: those (i) above 23 K, (ii) between 23 K and 8.5 K, and (iii) below 8.5 K. The linewidth is affected by the dynamics of Z2 vortices below 23 K and one of the conventional spiral resonance modes explains well the frequency dependence of the ESR resonance fields far below 8.5 K. Furthermore, we found an anomaly in the magnetization curve around one third of the saturation magnetization for H⊥c, corresponding to softening of another resonance mode. These results suggest the occurrence of a Z2 vortex-induced topological transition at 8.5 K. © 2008 The American Physical Society.
613.
M Kriener, Y Maeno, T Oguchi, Z -A Ren, J Kato, T Muranaka, J Akimitsu
Specific heat and electronic states of superconducting boron-doped silicon carbide Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 78, no. 2, 2008.
@article{Kriener2008,
title = {Specific heat and electronic states of superconducting boron-doped silicon carbide},
author = {M Kriener and Y Maeno and T Oguchi and Z -A Ren and J Kato and T Muranaka and J Akimitsu},
doi = {10.1103/PhysRevB.78.024517},
year = {2008},
date = {2008-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {78},
number = {2},
abstract = {The discoveries of superconductivity in the heavily-boron doped semiconductors diamond (C:B) in 2004 and silicon (Si:B) in 2006 have renewed the interest in the physics of the superconducting state of doped semiconductors. Recently, we discovered superconductivity in the closely related "mixed" system heavily boron-doped silcon carbide (SiC:B). Interestingly, the latter compound is a type-I superconductor whereas the two aforementioned materials are type II. In this paper, we present an extensive analysis of our recent specific-heat study, as well as the band structure and expected Fermi surfaces. We observe an apparent quadratic temperature dependence of the electronic specific heat in the superconducting state. Possible reasons are a nodal gap structure or a residual density of states due to nonsuperconducting parts of the sample. The basic superconducting parameters are estimated in a Ginzburg-Landau framework. We compare and discuss our results with those reported for C:B and Si:B. Finally, we comment on possible origins of the difference in the superconductivity of SiC:B compared to the two "parent" materials C:B and Si:B. © 2008 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The discoveries of superconductivity in the heavily-boron doped semiconductors diamond (C:B) in 2004 and silicon (Si:B) in 2006 have renewed the interest in the physics of the superconducting state of doped semiconductors. Recently, we discovered superconductivity in the closely related "mixed" system heavily boron-doped silcon carbide (SiC:B). Interestingly, the latter compound is a type-I superconductor whereas the two aforementioned materials are type II. In this paper, we present an extensive analysis of our recent specific-heat study, as well as the band structure and expected Fermi surfaces. We observe an apparent quadratic temperature dependence of the electronic specific heat in the superconducting state. Possible reasons are a nodal gap structure or a residual density of states due to nonsuperconducting parts of the sample. The basic superconducting parameters are estimated in a Ginzburg-Landau framework. We compare and discuss our results with those reported for C:B and Si:B. Finally, we comment on possible origins of the difference in the superconductivity of SiC:B compared to the two "parent" materials C:B and Si:B. © 2008 The American Physical Society.
612.
R Fittipaldi, A Vecchione, R Ciancio, S Pace, M Cuoco, D Stornaiuolo, D Born, F Tafuri, E Olsson, S Kittaka, H Yaguchi, Y Maeno
Superconductivity in Sr2RuO4-Sr3Ru 2O7 eutectic crystals Journal Article
In: EPL, vol. 83, no. 2, 2008.
@article{Fittipaldi2008,
title = {Superconductivity in Sr2RuO4-Sr3Ru 2O7 eutectic crystals},
author = {R Fittipaldi and A Vecchione and R Ciancio and S Pace and M Cuoco and D Stornaiuolo and D Born and F Tafuri and E Olsson and S Kittaka and H Yaguchi and Y Maeno},
doi = {10.1209/0295-5075/83/27007},
year = {2008},
date = {2008-01-01},
journal = {EPL},
volume = {83},
number = {2},
abstract = {Superconducting behavior has been observed in the Sr2RuO 4-Sr3Ru2O7 eutectic system as grown by the flux-feeding floating-zone technique. A supercurrent flows across a single interface between Sr2RuO4 and Sr3Ru 2O7 areas at distances that are far beyond those expected in a conventional proximity effect. The current-voltage characteristics within the Sr3Ru2O7 macrodomain, as extracted from the eutectic, exhibit signatures of superconductivity in the bilayered Sr 3Ru2O7 region. Detailed microstructural, morphological and compositional analyses address issues on the concentration and the size of Sr2RuO4 inclusions within the Sr 3Ru2O7 matrix. We speculate on the possibility of inhomogeneous superconductivity in the eutectic Sr3Ru 2O7 and exotic pairing induced by the Sr 2RuO4 inclusions. © Europhysics Letters Association.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Superconducting behavior has been observed in the Sr2RuO 4-Sr3Ru2O7 eutectic system as grown by the flux-feeding floating-zone technique. A supercurrent flows across a single interface between Sr2RuO4 and Sr3Ru 2O7 areas at distances that are far beyond those expected in a conventional proximity effect. The current-voltage characteristics within the Sr3Ru2O7 macrodomain, as extracted from the eutectic, exhibit signatures of superconductivity in the bilayered Sr 3Ru2O7 region. Detailed microstructural, morphological and compositional analyses address issues on the concentration and the size of Sr2RuO4 inclusions within the Sr 3Ru2O7 matrix. We speculate on the possibility of inhomogeneous superconductivity in the eutectic Sr3Ru 2O7 and exotic pairing induced by the Sr 2RuO4 inclusions. © Europhysics Letters Association.
611.
S Kittaka, S Fusanobori, S Yonezawa, H Yaguchi, Y Maeno, R Fittipaldi, A Vecchione
Multiple superconducting transitions in the Sr3 Ru2 O7 region of Sr3 Ru2 O7 -Sr2 Ru O4 eutectic crystals Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 77, no. 21, 2008.
@article{Kittaka2008,
title = {Multiple superconducting transitions in the Sr3 Ru2 O7 region of Sr3 Ru2 O7 -Sr2 Ru O4 eutectic crystals},
author = {S Kittaka and S Fusanobori and S Yonezawa and H Yaguchi and Y Maeno and R Fittipaldi and A Vecchione},
doi = {10.1103/PhysRevB.77.214511},
year = {2008},
date = {2008-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {77},
number = {21},
abstract = {We report the superconducting properties of Sr3 Ru2 O7 -Sr2 RuO4 eutectic crystals, which consist of the spin-triplet superconductor Sr2 RuO4 with a monolayer stacking of RuO2 planes and the metamagnetic normal metal Sr3 Ru2 O7 with a bilayer stacking. Although Sr3 Ru2 O7 so far has not been reported to exhibit superconductivity, our ac susceptibility measurements revealed multiple superconducting transitions that occur in the Sr3 Ru2 O7 region of the eutectic crystals. The diamagnetic shielding essentially reached the full fraction at low ac fields parallel to the c axis. However, both the shielding fraction and the onset temperature are easily suppressed by ac fields larger than 0.1 mT rms and no anomaly was observed in the specific heat. Moreover, the critical field curves of these transitions have a positive curvature near zero fields, which is different from the upper critical field curve of the bulk Sr2 RuO4. These facts suggest that the superconductivity observed in the Sr3 Ru2 O7 region is not a bulk property. To explain these experimental results, we propose the scenario that stacking RuO2 planes, which are the building blocks of superconducting Sr2 RuO4, are contained in the Sr3 Ru2 O7 region as stacking faults. © 2008 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report the superconducting properties of Sr3 Ru2 O7 -Sr2 RuO4 eutectic crystals, which consist of the spin-triplet superconductor Sr2 RuO4 with a monolayer stacking of RuO2 planes and the metamagnetic normal metal Sr3 Ru2 O7 with a bilayer stacking. Although Sr3 Ru2 O7 so far has not been reported to exhibit superconductivity, our ac susceptibility measurements revealed multiple superconducting transitions that occur in the Sr3 Ru2 O7 region of the eutectic crystals. The diamagnetic shielding essentially reached the full fraction at low ac fields parallel to the c axis. However, both the shielding fraction and the onset temperature are easily suppressed by ac fields larger than 0.1 mT rms and no anomaly was observed in the specific heat. Moreover, the critical field curves of these transitions have a positive curvature near zero fields, which is different from the upper critical field curve of the bulk Sr2 RuO4. These facts suggest that the superconductivity observed in the Sr3 Ru2 O7 region is not a bulk property. To explain these experimental results, we propose the scenario that stacking RuO2 planes, which are the building blocks of superconducting Sr2 RuO4, are contained in the Sr3 Ru2 O7 region as stacking faults. © 2008 The American Physical Society.
610.
K Kitagawa, R Higashinaka, K Ishida, Y Maeno, M Takigawa
High-temperature spin relaxation process in Dy2 Ti2 O7 probed by T 47 i-NQR Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 77, no. 21, 2008.
@article{Kitagawa2008,
title = {High-temperature spin relaxation process in Dy2 Ti2 O7 probed by T 47 i-NQR},
author = {K Kitagawa and R Higashinaka and K Ishida and Y Maeno and M Takigawa},
doi = {10.1103/PhysRevB.77.214403},
year = {2008},
date = {2008-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {77},
number = {21},
abstract = {We have performed nuclear quadrupole resonance (NQR) experiments on T 47 i nuclei in Dy2 Ti2 O7 in the temperature range of 70-300 K in order to investigate the dynamics of 4f electrons with strong Ising anisotropy. A significant change in the NQR frequency with temperature was attributed to the variation of the quadrupole moment of Dy4f electrons. A quantitative account was given by the mean-field analysis of the quadrupole-quadrupole (Q-Q) interaction in the presence of the crystalline-electric-field splitting. The magnitude and the temperature dependence of the nuclear spin-lattice relaxation rate were analyzed, including both the spin-spin and the Q-Q interactions. The results indicate that these two types of interaction contribute almost equally to the fluctuation of Dy magnetic moments. © 2008 The American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We have performed nuclear quadrupole resonance (NQR) experiments on T 47 i nuclei in Dy2 Ti2 O7 in the temperature range of 70-300 K in order to investigate the dynamics of 4f electrons with strong Ising anisotropy. A significant change in the NQR frequency with temperature was attributed to the variation of the quadrupole moment of Dy4f electrons. A quantitative account was given by the mean-field analysis of the quadrupole-quadrupole (Q-Q) interaction in the presence of the crystalline-electric-field splitting. The magnitude and the temperature dependence of the nuclear spin-lattice relaxation rate were analyzed, including both the spin-spin and the Q-Q interactions. The results indicate that these two types of interaction contribute almost equally to the fluctuation of Dy magnetic moments. © 2008 The American Physical Society.
609.
S Yonezawa, S Kusaba, Y Maeno, P Auban-Senzier, C Pasquier, D Jérome
Magnetic-field variations of the pair-breaking effects of superconductivity in (TMTSF)2ClO4 Journal Article
In: Journal of the Physical Society of Japan, vol. 77, no. 5, 2008.
@article{Yonezawa2008,
title = {Magnetic-field variations of the pair-breaking effects of superconductivity in (TMTSF)2ClO4},
author = {S Yonezawa and S Kusaba and Y Maeno and P Auban-Senzier and C Pasquier and D Jérome},
doi = {10.1143/JPSJ.77.054712},
year = {2008},
date = {2008-01-01},
journal = {Journal of the Physical Society of Japan},
volume = {77},
number = {5},
abstract = {We have studied the onset temperature of the superconductivity T conset of the organic superconductor (TMTSF) 2ClO4, by precisely controlling the direction of the magnetic field H. We compare the results of two samples with nearly the same onset temperature but with different scattering relaxation time τ. We revealed a complicated interplay of a variety of pair-breaking effects and mechanisms that overcome these pair-breaking effects. In low fields, the linear temperature dependences of the onset curves in the H-T phase diagrams are governed by the orbital pair-breaking effect. The dips in the in-plane field-angle φ dependence of Tconset, which were only observed in the long-τ sample, provides definitive evidence that the field-induced dimensional crossover enhances the superconductivity if the field direction is more than about 19° away from the a axis. In the high-field regime for H ∥ a, the upturn of the onset curve for the long-τ sample indicates a new superconducting state that overcomes the Pauli pair-breaking effect but is easily suppressed by impurity scatterings. The Pauli effect is also overcome for H ∥ b′ by a realization of another state for which the maximum of Tconset(φ) occurs in a direction different from the crystalline axes. The effect on Tconset of tilting the applied field out of the conductive plane suggests that the Pauli effect plays a significant role in determining Tc onset. The most plausible explanation of these results is that (TMTSF)2ClO4 is a singlet superconductor and exhibits Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states in high fields. ©2008 The Physical Society of Japan.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We have studied the onset temperature of the superconductivity T conset of the organic superconductor (TMTSF) 2ClO4, by precisely controlling the direction of the magnetic field H. We compare the results of two samples with nearly the same onset temperature but with different scattering relaxation time τ. We revealed a complicated interplay of a variety of pair-breaking effects and mechanisms that overcome these pair-breaking effects. In low fields, the linear temperature dependences of the onset curves in the H-T phase diagrams are governed by the orbital pair-breaking effect. The dips in the in-plane field-angle φ dependence of Tconset, which were only observed in the long-τ sample, provides definitive evidence that the field-induced dimensional crossover enhances the superconductivity if the field direction is more than about 19° away from the a axis. In the high-field regime for H ∥ a, the upturn of the onset curve for the long-τ sample indicates a new superconducting state that overcomes the Pauli pair-breaking effect but is easily suppressed by impurity scatterings. The Pauli effect is also overcome for H ∥ b′ by a realization of another state for which the maximum of Tconset(φ) occurs in a direction different from the crystalline axes. The effect on Tconset of tilting the applied field out of the conductive plane suggests that the Pauli effect plays a significant role in determining Tc onset. The most plausible explanation of these results is that (TMTSF)2ClO4 is a singlet superconductor and exhibits Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states in high fields. ©2008 The Physical Society of Japan.
608.
S K Goh, P L Alireza, P D A Mann, A -M Cumberlidge, C Bergemann, M Sutherland, Y Maeno
High pressure de Haas-van Alphen studies of Sr2RuO4 using an anvil cell Journal Article
In: Current Applied Physics, vol. 8, no. 3-4, pp. 304-307, 2008.
@article{Goh2008304,
title = {High pressure de Haas-van Alphen studies of Sr2RuO4 using an anvil cell},
author = {S K Goh and P L Alireza and P D A Mann and A -M Cumberlidge and C Bergemann and M Sutherland and Y Maeno},
doi = {10.1016/j.cap.2007.10.020},
year = {2008},
date = {2008-01-01},
journal = {Current Applied Physics},
volume = {8},
number = {3-4},
pages = {304-307},
abstract = {We have developed a novel way to perform de Haas-van Alphen (dHvA) measurements under high pressure using a microcoil system in an anvil cell, allowing us to track the electronic structure of strongly correlated electronic systems as a function of pressure. The unconventional superconductor Sr2RuO4 is chosen to illustrate the feasibility of this technique. The dHvA frequencies are obtained from the oscillatory data and they are compared with the values reported earlier in the literature. The quasiparticle effective masses are extracted from our high resolution dHvA data. © 2007 Elsevier B.V. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We have developed a novel way to perform de Haas-van Alphen (dHvA) measurements under high pressure using a microcoil system in an anvil cell, allowing us to track the electronic structure of strongly correlated electronic systems as a function of pressure. The unconventional superconductor Sr2RuO4 is chosen to illustrate the feasibility of this technique. The dHvA frequencies are obtained from the oscillatory data and they are compared with the values reported earlier in the literature. The quasiparticle effective masses are extracted from our high resolution dHvA data. © 2007 Elsevier B.V. All rights reserved.
607.
Y Nambu, M Ichihara, Y Kiuchi, S Nakatsuji, Y Maeno
Synthesis and characterization of the quasi-two-dimensional triangular antiferromagnets Ni1-xMxGa2S4 (M=Mn, Fe, Co, Zn) Journal Article
In: Journal of Crystal Growth, vol. 310, no. 7-9, pp. 1881-1885, 2008.
@article{Nambu20081881,
title = {Synthesis and characterization of the quasi-two-dimensional triangular antiferromagnets Ni1-xMxGa2S4 (M=Mn, Fe, Co, Zn)},
author = {Y Nambu and M Ichihara and Y Kiuchi and S Nakatsuji and Y Maeno},
doi = {10.1016/j.jcrysgro.2007.11.222},
year = {2008},
date = {2008-01-01},
journal = {Journal of Crystal Growth},
volume = {310},
number = {7-9},
pages = {1881-1885},
abstract = {Polycrystalline samples of Ni1-xMxGa2S4 (M=Mn, Fe, Co and Zn) have been synthesized by solid-state reaction. X-ray powder diffraction measurements indicate that these samples maintain the same trigonal structure as that of NiGa2S4 at least up to x=0.1 for M=Mn},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Polycrystalline samples of Ni1-xMxGa2S4 (M=Mn, Fe, Co and Zn) have been synthesized by solid-state reaction. X-ray powder diffraction measurements indicate that these samples maintain the same trigonal structure as that of NiGa2S4 at least up to x=0.1 for M=Mn
606.
K Tenya, R Yamahana, M Yokoyama, H Amitsuka, K Deguchi, Y Maeno
Anomalous pinning behavior in Sr2 RuO4 Journal Article
In: Physica B: Condensed Matter, vol. 403, no. 5-9, pp. 1101-1103, 2008.
@article{Tenya20081101,
title = {Anomalous pinning behavior in Sr2 RuO4},
author = {K Tenya and R Yamahana and M Yokoyama and H Amitsuka and K Deguchi and Y Maeno},
doi = {10.1016/j.physb.2007.10.096},
year = {2008},
date = {2008-01-01},
journal = {Physica B: Condensed Matter},
volume = {403},
number = {5-9},
pages = {1101-1103},
abstract = {In order to investigate the chiral-superconducting characteristics as well as the vortex-pinning properties, detailed magnetization measurements of the single crystal Sr2 RuO4 have been performed in the field parallel to the [0 0 1] direction. Anomalous pinning features are found at weak fields in the magnetization curves: Tiny flux-jumps successively appear around zero field at temperatures up to at least 0.2 K. At higher temperatures, a small peak of the hysteretic magnetization is observed below 0.1 kOe, which is so-called second magnetization peak (SMP). The magnitude of the hysteretic magnetization is strongly dependent on (independent of) the field-gradient in the field region below (above) the field where the SMP appears. Possible origins are discussed from the viewpoints of the pairing symmetry together with the topological change in the vortex-lattice configuration. © 2007 Elsevier B.V. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In order to investigate the chiral-superconducting characteristics as well as the vortex-pinning properties, detailed magnetization measurements of the single crystal Sr2 RuO4 have been performed in the field parallel to the [0 0 1] direction. Anomalous pinning features are found at weak fields in the magnetization curves: Tiny flux-jumps successively appear around zero field at temperatures up to at least 0.2 K. At higher temperatures, a small peak of the hysteretic magnetization is observed below 0.1 kOe, which is so-called second magnetization peak (SMP). The magnitude of the hysteretic magnetization is strongly dependent on (independent of) the field-gradient in the field region below (above) the field where the SMP appears. Possible origins are discussed from the viewpoints of the pairing symmetry together with the topological change in the vortex-lattice configuration. © 2007 Elsevier B.V. All rights reserved.
605.
S Ramos, E M Forgan, C Bowell, S M Hayden, A J Schofield, A Wildes, E A Yelland, S P Brown, M Laver, R S Perry, Y Maeno
Spin dynamics in Sr3 Ru2 O7 near the metamagnetic transition by inelastic neutron scattering Journal Article
In: Physica B: Condensed Matter, vol. 403, no. 5-9, pp. 1270-1272, 2008.
@article{Ramos20081270,
title = {Spin dynamics in Sr3 Ru2 O7 near the metamagnetic transition by inelastic neutron scattering},
author = {S Ramos and E M Forgan and C Bowell and S M Hayden and A J Schofield and A Wildes and E A Yelland and S P Brown and M Laver and R S Perry and Y Maeno},
doi = {10.1016/j.physb.2007.10.123},
year = {2008},
date = {2008-01-01},
journal = {Physica B: Condensed Matter},
volume = {403},
number = {5-9},
pages = {1270-1272},
abstract = {The bilayered ruthenate Sr3 Ru2 O7 has a metamagnetic quantum critical point. This is the first example of a material with a quantum-critical end-point. This work addresses the problem of the metamagnetic criticality in this system through the measurement of spin fluctuations by inelastic neutron scattering. Our results show that incommensurate antiferromagnetic fluctuations are present in a wide range of applied fields. We have also observed how ferromagnetic fluctuations develop at the metamagnetic field. Finally, the intensity of the two types of fluctuations is followed as a function of the energy transfer between the neutron and the spins. © 2007 Elsevier B.V. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The bilayered ruthenate Sr3 Ru2 O7 has a metamagnetic quantum critical point. This is the first example of a material with a quantum-critical end-point. This work addresses the problem of the metamagnetic criticality in this system through the measurement of spin fluctuations by inelastic neutron scattering. Our results show that incommensurate antiferromagnetic fluctuations are present in a wide range of applied fields. We have also observed how ferromagnetic fluctuations develop at the metamagnetic field. Finally, the intensity of the two types of fluctuations is followed as a function of the energy transfer between the neutron and the spins. © 2007 Elsevier B.V. All rights reserved.
604.
K Kawashima, M Kriener, M Ishii, Y Maeno, J Akimitsu
Thermodynamic properties of the clathrate-type silver-oxide Ag6O8AgHF2 Journal Article
In: Physica C: Superconductivity and its Applications, vol. 468, no. 6, pp. 464-470, 2008.
@article{Kawashima2008464,
title = {Thermodynamic properties of the clathrate-type silver-oxide Ag6O8AgHF2},
author = {K Kawashima and M Kriener and M Ishii and Y Maeno and J Akimitsu},
doi = {10.1016/j.physc.2008.01.008},
year = {2008},
date = {2008-01-01},
journal = {Physica C: Superconductivity and its Applications},
volume = {468},
number = {6},
pages = {464-470},
abstract = {We report normal-state and superconducting properties of the clathrate-type silver-oxide Ag6O8AgHF2. We present electrical resistivity, DC- and AC-susceptibility and specific-heat measurements of single crystalline Ag6O8AgHF2. In the normal state, Ag6O8AgHF2 exhibits metallic conductivity and a phase transition near 110 K, possibly a structural phase transition as observed in the related compound Ag6O8AgNO3. The onset of superconductivity of our samples is observed around 1.2-1.5 K, and the H-T phase diagram is determined for the first time. The upper critical field Hc2(0) is estimated to be about 2000-2200 Oe and the coherence length ξGL(0) to be 40 nm. © 2008 Elsevier B.V. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report normal-state and superconducting properties of the clathrate-type silver-oxide Ag6O8AgHF2. We present electrical resistivity, DC- and AC-susceptibility and specific-heat measurements of single crystalline Ag6O8AgHF2. In the normal state, Ag6O8AgHF2 exhibits metallic conductivity and a phase transition near 110 K, possibly a structural phase transition as observed in the related compound Ag6O8AgNO3. The onset of superconductivity of our samples is observed around 1.2-1.5 K, and the H-T phase diagram is determined for the first time. The upper critical field Hc2(0) is estimated to be about 2000-2200 Oe and the coherence length ξGL(0) to be 40 nm. © 2008 Elsevier B.V. All rights reserved.
