2013
753.
H Taniguchi, K Nishimura, R Ishikawa, S Yonezawa, S K Goh, F Nakamura, Y Maeno
Anisotropic uniaxial pressure response of the Mott insulator Ca 2RuO4 Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 88, no. 20, 2013.
@article{Taniguchi2013,
title = {Anisotropic uniaxial pressure response of the Mott insulator Ca 2RuO4},
author = {H Taniguchi and K Nishimura and R Ishikawa and S Yonezawa and S K Goh and F Nakamura and Y Maeno},
doi = {10.1103/PhysRevB.88.205111},
year = {2013},
date = {2013-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {88},
number = {20},
abstract = {We have investigated the in-plane uniaxial pressure effect on the antiferromagnetic Mott insulator Ca2RuO4 from resistivity and magnetization measurements. We succeeded in inducing the ferromagnetic metallic phase at lower critical pressure than by hydrostatic pressure, indicating that the flattening distortion of the RuO6 octahedra is more easily released under in-plane uniaxial pressure. We also found a striking in-plane anisotropy in the pressure responses of various magnetic phases: although the magnetization increases monotonically with pressure diagonal to the orthorhombic principal axes, the magnetization exhibits peculiar dependence on pressure along the in-plane orthorhombic principal axes. This peculiar dependence can be explained by a qualitative difference between the uniaxial pressure effects along the orthorhombic a and b axes, as well as by the presence of twin domain structures. © 2013 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We have investigated the in-plane uniaxial pressure effect on the antiferromagnetic Mott insulator Ca2RuO4 from resistivity and magnetization measurements. We succeeded in inducing the ferromagnetic metallic phase at lower critical pressure than by hydrostatic pressure, indicating that the flattening distortion of the RuO6 octahedra is more easily released under in-plane uniaxial pressure. We also found a striking in-plane anisotropy in the pressure responses of various magnetic phases: although the magnetization increases monotonically with pressure diagonal to the orthorhombic principal axes, the magnetization exhibits peculiar dependence on pressure along the in-plane orthorhombic principal axes. This peculiar dependence can be explained by a qualitative difference between the uniaxial pressure effects along the orthorhombic a and b axes, as well as by the presence of twin domain structures. © 2013 American Physical Society.
752.
J A Sobota, K Kim, H Takatsu, M Hashimoto, S -K Mo, Z Hussain, T Oguchi, T Shishidou, Y Maeno, B I Min, Z -X Shen
Electronic structure of the metallic antiferromagnet PdCrO2 measured by angle-resolved photoemission spectroscopy Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 88, no. 12, 2013.
@article{Sobota2013,
title = {Electronic structure of the metallic antiferromagnet PdCrO2 measured by angle-resolved photoemission spectroscopy},
author = {J A Sobota and K Kim and H Takatsu and M Hashimoto and S -K Mo and Z Hussain and T Oguchi and T Shishidou and Y Maeno and B I Min and Z -X Shen},
doi = {10.1103/PhysRevB.88.125109},
year = {2013},
date = {2013-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {88},
number = {12},
abstract = {PdCrO2 is material which has attracted interest due to the coexistence of metallic conductivity associated with itinerant Pd 4d electrons and antiferromagnetic order arising from localized Cr spins. A central issue is determining to what extent the magnetic order couples to the conduction electrons. Here we perform angle-resolved photoemission spectroscopy (ARPES) to experimentally characterize the electronic structure. We find that the Fermi surface has contributions from both bulk and surface states, which can be experimentally distinguished and theoretically verified by slab band structure calculations. The bulk Fermi surface shows no signature of electronic reconstruction in the antiferromagnetic state. This observation suggests that there is negligible interaction between the localized Cr spin structure and the itinerant Pd electrons measured by ARPES. © 2013 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
PdCrO2 is material which has attracted interest due to the coexistence of metallic conductivity associated with itinerant Pd 4d electrons and antiferromagnetic order arising from localized Cr spins. A central issue is determining to what extent the magnetic order couples to the conduction electrons. Here we perform angle-resolved photoemission spectroscopy (ARPES) to experimentally characterize the electronic structure. We find that the Fermi surface has contributions from both bulk and surface states, which can be experimentally distinguished and theoretically verified by slab band structure calculations. The bulk Fermi surface shows no signature of electronic reconstruction in the antiferromagnetic state. This observation suggests that there is negligible interaction between the localized Cr spin structure and the itinerant Pd electrons measured by ARPES. © 2013 American Physical Society.
751.
M S Anwar, T Nakamura, S Yonezawa, M Yakabe, R Ishiguro, H Takayanagi, Y Maeno
Anomalous switching in Nb/Ru/Sr2 RuO4 topological junctions by chiral domain wall motion Journal Article
In: Scientific Reports, vol. 3, 2013.
@article{Anwar2013,
title = {Anomalous switching in Nb/Ru/Sr2 RuO4 topological junctions by chiral domain wall motion},
author = {M S Anwar and T Nakamura and S Yonezawa and M Yakabe and R Ishiguro and H Takayanagi and Y Maeno},
doi = {10.1038/srep02480},
year = {2013},
date = {2013-01-01},
journal = {Scientific Reports},
volume = {3},
abstract = {A spontaneous symmetry breaking in a system often results in domain wall formation. The motion of such domain walls is utilized to realize novel devices like racetrack-memories, in which moving ferromagnetic domain walls store and carry information. Superconductors breaking time reversal symmetry can also form domains with degenerate chirality of their superconducting order parameter. Sr2 RuO4 is the leading candidate of a chiral p-wave superconductor, expected to be accompanied by chiral domain structure. Here, we present that Nb/Ru/Sr2 RuO4 topological superconducting-junctions, with which the phase winding of order parameter can be effectively probed by making use of real-space topology, exhibit unusual switching between higher and lower critical current states. This switching is well explained by chiral-domain-wall dynamics. The switching can be partly controlled by external parameters such as temperature, magnetic field and current. These results open up a possibility to utilize the superconducting chiral domain wall motion for future novel superconducting devices. © 2013 Macmillan Publishers Limited.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
A spontaneous symmetry breaking in a system often results in domain wall formation. The motion of such domain walls is utilized to realize novel devices like racetrack-memories, in which moving ferromagnetic domain walls store and carry information. Superconductors breaking time reversal symmetry can also form domains with degenerate chirality of their superconducting order parameter. Sr2 RuO4 is the leading candidate of a chiral p-wave superconductor, expected to be accompanied by chiral domain structure. Here, we present that Nb/Ru/Sr2 RuO4 topological superconducting-junctions, with which the phase winding of order parameter can be effectively probed by making use of real-space topology, exhibit unusual switching between higher and lower critical current states. This switching is well explained by chiral-domain-wall dynamics. The switching can be partly controlled by external parameters such as temperature, magnetic field and current. These results open up a possibility to utilize the superconducting chiral domain wall motion for future novel superconducting devices. © 2013 Macmillan Publishers Limited.
750.
F Nakamura, M Sakaki, Y Yamanaka, S Tamaru, T Suzuki, Y Maeno
Electric-field-induced metal maintained by current of the Mott insulator Ca2RuO4 Journal Article
In: Scientific Reports, vol. 3, 2013.
@article{Nakamura2013,
title = {Electric-field-induced metal maintained by current of the Mott insulator Ca2RuO4},
author = {F Nakamura and M Sakaki and Y Yamanaka and S Tamaru and T Suzuki and Y Maeno},
doi = {10.1038/srep02536},
year = {2013},
date = {2013-01-01},
journal = {Scientific Reports},
volume = {3},
abstract = {Recently, "application of electric field (E-field)" has received considerable attention as a new method to induce novel quantum phenomena since application of E-field can tune the electronic states directly with obvious scientific and industrial advantages over other turning methods. However, E-field-induced Mott transitions are rare and typically require high E-field and low temperature. Here we report that the multiband Mott insulator Ca2RuO4 shows unique insulator-metal switching induced by applying a dry-battery level voltage at room temperature. The threshold field Eth ∼40 V/cm is much weaker than the Mott gap energy. Moreover, the switching is accompanied by a bulk structural transition. Perhaps the most peculiar of the present findings is that the induced metal can be maintained to low temperature by a weak current.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Recently, "application of electric field (E-field)" has received considerable attention as a new method to induce novel quantum phenomena since application of E-field can tune the electronic states directly with obvious scientific and industrial advantages over other turning methods. However, E-field-induced Mott transitions are rare and typically require high E-field and low temperature. Here we report that the multiband Mott insulator Ca2RuO4 shows unique insulator-metal switching induced by applying a dry-battery level voltage at room temperature. The threshold field Eth ∼40 V/cm is much weaker than the Mott gap energy. Moreover, the switching is accompanied by a bulk structural transition. Perhaps the most peculiar of the present findings is that the induced metal can be maintained to low temperature by a weak current.
749.
C Rastovski, C D Dewhurst, W J Gannon, D C Peets, H Takatsu, Y Maeno, M Ichioka, K Machida, M R Eskildsen
Anisotropy of the superconducting state in Sr2RuO4 Journal Article
In: Physical Review Letters, vol. 111, no. 8, 2013.
@article{Rastovski2013,
title = {Anisotropy of the superconducting state in Sr2RuO4},
author = {C Rastovski and C D Dewhurst and W J Gannon and D C Peets and H Takatsu and Y Maeno and M Ichioka and K Machida and M R Eskildsen},
doi = {10.1103/PhysRevLett.111.087003},
year = {2013},
date = {2013-01-01},
journal = {Physical Review Letters},
volume = {111},
number = {8},
abstract = {Despite intense studies the exact nature of the order parameter in superconducting Sr2RuO4 remains unresolved. We have used small-angle neutron scattering to study the vortex lattice in Sr 2RuO4 with the field applied close to the basal plane, taking advantage of the transverse magnetization. We measured the intrinsic superconducting anisotropy between the c axis and the Ru-O basal plane (∼60), which greatly exceeds the upper critical field anisotropy (∼20). Our result imposes significant constraints on possible models of triplet pairing in Sr2RuO4 and raises questions concerning the direction of the zero spin projection axis. © 2013 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Despite intense studies the exact nature of the order parameter in superconducting Sr2RuO4 remains unresolved. We have used small-angle neutron scattering to study the vortex lattice in Sr 2RuO4 with the field applied close to the basal plane, taking advantage of the transverse magnetization. We measured the intrinsic superconducting anisotropy between the c axis and the Ru-O basal plane (∼60), which greatly exceeds the upper critical field anisotropy (∼20). Our result imposes significant constraints on possible models of triplet pairing in Sr2RuO4 and raises questions concerning the direction of the zero spin projection axis. © 2013 American Physical Society.
748.
H Takatsu, J J Ishikawa, S Yonezawa, H Yoshino, T Shishidou, T Oguchi, K Murata, Y Maeno
Extremely large magnetoresistance in the nonmagnetic metal PdCoO 2 Journal Article
In: Physical Review Letters, vol. 111, no. 5, 2013.
@article{Takatsu2013,
title = {Extremely large magnetoresistance in the nonmagnetic metal PdCoO 2},
author = {H Takatsu and J J Ishikawa and S Yonezawa and H Yoshino and T Shishidou and T Oguchi and K Murata and Y Maeno},
doi = {10.1103/PhysRevLett.111.056601},
year = {2013},
date = {2013-01-01},
journal = {Physical Review Letters},
volume = {111},
number = {5},
abstract = {Extremely large magnetoresistance is realized in the nonmagnetic layered metal PdCoO2. In spite of a highly conducting metallic behavior with a simple quasi-two-dimensional hexagonal Fermi surface, the interlayer resistance reaches up to 35 000% for the field along the [11̄0] direction. Furthermore, the temperature dependence of the resistance becomes nonmetallic for this field direction, while it remains metallic for fields along the [110] direction. Such severe and anisotropic destruction of the interlayer coherence by a magnetic field on a simple Fermi surface is ascribable to orbital motion of carriers on the Fermi surface driven by the Lorentz force, but seems to have been largely overlooked until now. © 2013 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Extremely large magnetoresistance is realized in the nonmagnetic layered metal PdCoO2. In spite of a highly conducting metallic behavior with a simple quasi-two-dimensional hexagonal Fermi surface, the interlayer resistance reaches up to 35 000% for the field along the [11̄0] direction. Furthermore, the temperature dependence of the resistance becomes nonmetallic for this field direction, while it remains metallic for fields along the [110] direction. Such severe and anisotropic destruction of the interlayer coherence by a magnetic field on a simple Fermi surface is ascribable to orbital motion of carriers on the Fermi surface driven by the Lorentz force, but seems to have been largely overlooked until now. © 2013 American Physical Society.
747.
S Tsuda, N Kikugawa, K Sugii, S Uji, S Ueda, M Nishio, Y Maeno
Mott transition extremely sensitive to impurities in Ca3Ru 2O7 revealed by hard x-ray photoemission studies Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 87, no. 24, 2013.
@article{Tsuda2013,
title = {Mott transition extremely sensitive to impurities in Ca3Ru 2O7 revealed by hard x-ray photoemission studies},
author = {S Tsuda and N Kikugawa and K Sugii and S Uji and S Ueda and M Nishio and Y Maeno},
doi = {10.1103/PhysRevB.87.241107},
year = {2013},
date = {2013-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {87},
number = {24},
abstract = {Hard x-ray photoemission studies of Ca3(Ru1-xTi x)2O7 with x = 0, 0.003, and 0.005 have been carried out to clarify the origin of the extremely high sensitivity of the metal-insulator (M-I) transition to the amount of Ti substitution. All the compounds show an antiferromagnetic transition followed by a structural transition at a temperature TS, with decreasing temperature. For x > 0, the structural transition is accompanied with a drastic M-I transition and the intensities of the screened peaks in the Ru 3d core-level spectra are significantly reduced below TS. The spectral weight of the valence band is concurrently shifted toward the higher binding energy side by an order of 2 eV, which shows that a strong electron correlation plays an essential role for the M-I transition at TS for x > 0. These results provide strong evidence that Mott transition is induced by a minute amount of the Ti substitution in Ca3Ru2O7. © 2013 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Hard x-ray photoemission studies of Ca3(Ru1-xTi x)2O7 with x = 0, 0.003, and 0.005 have been carried out to clarify the origin of the extremely high sensitivity of the metal-insulator (M-I) transition to the amount of Ti substitution. All the compounds show an antiferromagnetic transition followed by a structural transition at a temperature TS, with decreasing temperature. For x > 0, the structural transition is accompanied with a drastic M-I transition and the intensities of the screened peaks in the Ru 3d core-level spectra are significantly reduced below TS. The spectral weight of the valence band is concurrently shifted toward the higher binding energy side by an order of 2 eV, which shows that a strong electron correlation plays an essential role for the M-I transition at TS for x > 0. These results provide strong evidence that Mott transition is induced by a minute amount of the Ti substitution in Ca3Ru2O7. © 2013 American Physical Society.
746.
E J Patiño, M Aprili, M G Blamire, Y Maeno
Vortex flipping in superconductor/ferromagnet spin-valve structures Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 87, no. 21, 2013.
@article{Patiño2013,
title = {Vortex flipping in superconductor/ferromagnet spin-valve structures},
author = {E J Patiño and M Aprili and M G Blamire and Y Maeno},
doi = {10.1103/PhysRevB.87.214514},
year = {2013},
date = {2013-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {87},
number = {21},
abstract = {We report in-plane magnetization measurements on Ni/Nb/Ni/CoO and Co/Nb/Co/CoO spin valve structures with one of the ferromagnetic layers pinned by an antiferromagnetic layer. In samples with Ni below the superconducting transition Tc, our results show strong evidence of vortex flipping driven by ferromagnet magnetization. This is a direct consequence of the proximity effect that leads to vortex supercurrent leakage into the ferromagnets. Here, the polarized electron spins are subject to the vortices' magnetic field, occasioning vortex flipping. Such a novel mechanism has been made possible by fabrication of the ferromagnet/superconductor/ferromagnet/ antiferromagnet multilayered spin valves with an S layer thin enough to barely confine vortices inside as well as F layers thin enough to align and control magnetization within the plane. When Co is used, the vortex flipping effect is not observed. This is attributed to the shorter coherence length of Co. Interestingly, a reduction in the pinning field of about 400 Oe is observed instead when the Nb layer is in the superconducting state. This effect cannot be explained in terms of vortex fields. In view of these facts, any explanation must be directly related to the proximity effect and thus a remarkable phenomenon that deserves further investigation. © 2013 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report in-plane magnetization measurements on Ni/Nb/Ni/CoO and Co/Nb/Co/CoO spin valve structures with one of the ferromagnetic layers pinned by an antiferromagnetic layer. In samples with Ni below the superconducting transition Tc, our results show strong evidence of vortex flipping driven by ferromagnet magnetization. This is a direct consequence of the proximity effect that leads to vortex supercurrent leakage into the ferromagnets. Here, the polarized electron spins are subject to the vortices' magnetic field, occasioning vortex flipping. Such a novel mechanism has been made possible by fabrication of the ferromagnet/superconductor/ferromagnet/ antiferromagnet multilayered spin valves with an S layer thin enough to barely confine vortices inside as well as F layers thin enough to align and control magnetization within the plane. When Co is used, the vortex flipping effect is not observed. This is attributed to the shorter coherence length of Co. Interestingly, a reduction in the pinning field of about 400 Oe is observed instead when the Nb layer is in the superconducting state. This effect cannot be explained in terms of vortex fields. In view of these facts, any explanation must be directly related to the proximity effect and thus a remarkable phenomenon that deserves further investigation. © 2013 American Physical Society.
745.
G Bao, Y Inada, G Eguchi, Y Maeno, M Ichioka, G -Q Zheng
Influence on superconductivity in the parity mixing superconductor Li 2T3B(T:Pt,Pd) by non-magnetic impurity and defect doping Journal Article
In: Physica C: Superconductivity and its Applications, vol. 494, pp. 95-98, 2013.
@article{Bao201395,
title = {Influence on superconductivity in the parity mixing superconductor Li 2T3B(T:Pt,Pd) by non-magnetic impurity and defect doping},
author = {G Bao and Y Inada and G Eguchi and Y Maeno and M Ichioka and G -Q Zheng},
doi = {10.1016/j.physc.2013.04.059},
year = {2013},
date = {2013-01-01},
journal = {Physica C: Superconductivity and its Applications},
volume = {494},
pages = {95-98},
abstract = {Superconductors with noncentrosymmetric crystal structures such as Li 2T3B(T:Pd,Pt) have been the focus of in-depth research with their parity mixing nature. In this study, we focused our research on non-magnetic impurity effect in Li2T3B(T:Pd,Pt). The nature of the pair breaking by non-magnetic impurity in the parity mixing superconducting state is still unclear. We prepared different quality samples of Li2Pd3B and Li2Pt3B by changing conditions in synthesizing, and sample qualities were estimated by residual resistivity. Spin singlet dominant superconductor Li2Pd3B exhibits the weak Tc suppression attributed by non-magnetic impurity and defects, while Hc2 (0) value increased. This behavior is similar in ordinary s-wave superconductor. On the other hand, for the spin triplet dominant superconductor Li2Pt3B, it was suggested that the Cooper pair was broken and superconducting gap was decreased by non-magnetic impurities and defects. Li2Pt3B is similar to unconventional superconducting state. © 2013 Elsevier B.V. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Superconductors with noncentrosymmetric crystal structures such as Li 2T3B(T:Pd,Pt) have been the focus of in-depth research with their parity mixing nature. In this study, we focused our research on non-magnetic impurity effect in Li2T3B(T:Pd,Pt). The nature of the pair breaking by non-magnetic impurity in the parity mixing superconducting state is still unclear. We prepared different quality samples of Li2Pd3B and Li2Pt3B by changing conditions in synthesizing, and sample qualities were estimated by residual resistivity. Spin singlet dominant superconductor Li2Pd3B exhibits the weak Tc suppression attributed by non-magnetic impurity and defects, while Hc2 (0) value increased. This behavior is similar in ordinary s-wave superconductor. On the other hand, for the spin triplet dominant superconductor Li2Pt3B, it was suggested that the Cooper pair was broken and superconducting gap was decreased by non-magnetic impurities and defects. Li2Pt3B is similar to unconventional superconducting state. © 2013 Elsevier B.V. All rights reserved.
744.
G Eguchi, D C Peets, M Kriener, S Yonezawa, G Bao, S Harada, Y Inada, G -Q Zheng, Y Maeno
Phonon anomaly and anisotropic superconducting gap in noncentrosymmetric Li2(Pd1-xPtx)3B Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 87, no. 16, 2013.
@article{Eguchi2013,
title = {Phonon anomaly and anisotropic superconducting gap in noncentrosymmetric Li2(Pd1-xPtx)3B},
author = {G Eguchi and D C Peets and M Kriener and S Yonezawa and G Bao and S Harada and Y Inada and G -Q Zheng and Y Maeno},
doi = {10.1103/PhysRevB.87.161203},
year = {2013},
date = {2013-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {87},
number = {16},
abstract = {We report the systematic investigation of the specific heat of the noncentrosymmetric superconductor Li2(Pd1-xPtx)3B as a function of x. There is a large deviation of the phononic specific heat from the conventional Debye specific heat for Pt-rich samples. In contrast with the fully gapped conventional behavior for small x, a power-law temperature dependence of the electronic specific heat is observed even at x=0.5. These results manifest a strongly anisotropic or nodal superconducting gap even at x=0.5 and a nodal superconducting gap for xâ‰30.9. © 2013 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report the systematic investigation of the specific heat of the noncentrosymmetric superconductor Li2(Pd1-xPtx)3B as a function of x. There is a large deviation of the phononic specific heat from the conventional Debye specific heat for Pt-rich samples. In contrast with the fully gapped conventional behavior for small x, a power-law temperature dependence of the electronic specific heat is observed even at x=0.5. These results manifest a strongly anisotropic or nodal superconducting gap even at x=0.5 and a nodal superconducting gap for xâ‰30.9. © 2013 American Physical Society.
743.
C Stingl, R S Perry, Y Maeno, P Gegenwart
Electronic nematicity and its relation to quantum criticality in Sr3Ru2O7 studied by thermal expansion Journal Article
In: Physica Status Solidi (B) Basic Research, vol. 250, no. 3, pp. 450-456, 2013.
@article{Stingl2013450,
title = {Electronic nematicity and its relation to quantum criticality in Sr3Ru2O7 studied by thermal expansion},
author = {C Stingl and R S Perry and Y Maeno and P Gegenwart},
doi = {10.1002/pssb.201200905},
year = {2013},
date = {2013-01-01},
journal = {Physica Status Solidi (B) Basic Research},
volume = {250},
number = {3},
pages = {450-456},
abstract = {We report high-resolution measurements of the in-plane thermal expansion anisotropy in the vicinity of the electronic nematic phase in Sr3Ru2O7 down to very low temperatures and in varying magnetic field orientation. For fields applied along the c-direction, a clear second-order phase transition is found at the nematic phase, with critical behavior compatible with the two-dimensional Ising universality class (although this is not fully conclusive). Measurements in a slightly tilted magnetic field reveal a broken fourfold in-plane rotational symmetry, not only within the nematic phase, but extending towards slightly larger fields. We also analyze the universal scaling behavior expected for a metamagnetic quantum critical point, which is realized outside the nematic region. The contours of the magnetostriction suggest a relation between quantum criticality and the nematic phase. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report high-resolution measurements of the in-plane thermal expansion anisotropy in the vicinity of the electronic nematic phase in Sr3Ru2O7 down to very low temperatures and in varying magnetic field orientation. For fields applied along the c-direction, a clear second-order phase transition is found at the nematic phase, with critical behavior compatible with the two-dimensional Ising universality class (although this is not fully conclusive). Measurements in a slightly tilted magnetic field reveal a broken fourfold in-plane rotational symmetry, not only within the nematic phase, but extending towards slightly larger fields. We also analyze the universal scaling behavior expected for a metamagnetic quantum critical point, which is realized outside the nematic region. The contours of the magnetostriction suggest a relation between quantum criticality and the nematic phase. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
742.
C N Veenstra, Z -H Zhu, B Ludbrook, M Capsoni, G Levy, A Nicolaou, J A Rosen, R Comin, S Kittaka, Y Maeno, I S Elfimov, A Damascelli
In: Physical Review Letters, vol. 110, no. 9, 2013.
@article{Veenstra2013b,
title = {Determining the surface-to-bulk progression in the normal-state electronic structure of Sr2RuO4 by angle-resolved photoemission and density functional theory},
author = {C N Veenstra and Z -H Zhu and B Ludbrook and M Capsoni and G Levy and A Nicolaou and J A Rosen and R Comin and S Kittaka and Y Maeno and I S Elfimov and A Damascelli},
doi = {10.1103/PhysRevLett.110.097004},
year = {2013},
date = {2013-01-01},
journal = {Physical Review Letters},
volume = {110},
number = {9},
abstract = {We revisit the normal-state electronic structure of Sr2RuO 4 by angle-resolved photoemission spectroscopy with improved data quality, as well as ab initio band structure calculations in the local-density approximation with the inclusion of spin-orbit coupling. We find that the current model of a single surface layer (√2×√2)R45 reconstruction does not explain all detected features. The observed depth-dependent signal degradation, together with the close quantitative agreement with the slab calculations based on the surface crystal structure as determined by low-energy electron diffraction, reveal that - at a minimum - the subsurface layer also undergoes a similar although weaker reconstruction. This model accounts for all features - a key step in understanding the electronic structure - and indicates a surface-to-bulk progression of the electronic states driven by structural instabilities. Finally, we find no evidence for other phases stemming from either topological bulk properties or, alternatively, the interplay between spin-orbit coupling and the broken symmetry of the surface. © 2013 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We revisit the normal-state electronic structure of Sr2RuO 4 by angle-resolved photoemission spectroscopy with improved data quality, as well as ab initio band structure calculations in the local-density approximation with the inclusion of spin-orbit coupling. We find that the current model of a single surface layer (√2×√2)R45 reconstruction does not explain all detected features. The observed depth-dependent signal degradation, together with the close quantitative agreement with the slab calculations based on the surface crystal structure as determined by low-energy electron diffraction, reveal that - at a minimum - the subsurface layer also undergoes a similar although weaker reconstruction. This model accounts for all features - a key step in understanding the electronic structure - and indicates a surface-to-bulk progression of the electronic states driven by structural instabilities. Finally, we find no evidence for other phases stemming from either topological bulk properties or, alternatively, the interplay between spin-orbit coupling and the broken symmetry of the surface. © 2013 American Physical Society.
741.
C Stock, S Jonas, C Broholm, S Nakatsuji, Y Nambu, K Onuma, Y Maeno, J -H Chung
In: Physical Review Letters, vol. 110, no. 9, 2013.
@article{Stock2013,
title = {Erratum: Neutron-Scattering Measurement of Incommensurate Short-Range Order in Single Crystals of the S=1 Triangular Antiferromagnet NiGa2S 4 (Physical Review Letters (2010) 105 (037402) DOI:10.1103/ PhysRevLett.105.037402)},
author = {C Stock and S Jonas and C Broholm and S Nakatsuji and Y Nambu and K Onuma and Y Maeno and J -H Chung},
doi = {10.1103/PhysRevLett.110.099901},
year = {2013},
date = {2013-01-01},
journal = {Physical Review Letters},
volume = {110},
number = {9},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
740.
S Yonezawa, T Kajikawa, Y Maeno
First-order superconducting transition of Sr2RuO4 Journal Article
In: Physical Review Letters, vol. 110, no. 7, 2013.
@article{Yonezawa2013b,
title = {First-order superconducting transition of Sr2RuO4},
author = {S Yonezawa and T Kajikawa and Y Maeno},
doi = {10.1103/PhysRevLett.110.077003},
year = {2013},
date = {2013-01-01},
journal = {Physical Review Letters},
volume = {110},
number = {7},
abstract = {By means of the magnetocaloric effect, we examine the nature of the superconducting-normal (S-N) transition of Sr2RuO4, a most promising candidate for a spin-triplet superconductor. We provide thermodynamic evidence that the S-N transition of this oxide is of first order below approximately 0.8 K and only for magnetic field directions very close to the conducting plane, in clear contrast to the ordinary type-II superconductors exhibiting second-order S-N transitions. The entropy release across the transition at 0.2 K is 10% of the normal-state entropy. Our result urges an introduction of a new mechanism to break superconductivity by magnetic field. © 2013 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
By means of the magnetocaloric effect, we examine the nature of the superconducting-normal (S-N) transition of Sr2RuO4, a most promising candidate for a spin-triplet superconductor. We provide thermodynamic evidence that the S-N transition of this oxide is of first order below approximately 0.8 K and only for magnetic field directions very close to the conducting plane, in clear contrast to the ordinary type-II superconductors exhibiting second-order S-N transitions. The entropy release across the transition at 0.2 K is 10% of the normal-state entropy. Our result urges an introduction of a new mechanism to break superconductivity by magnetic field. © 2013 American Physical Society.
739.
M Mizumaki, T Mizokawa, A Agui, S Tanaka, H Takatsu, S Yonezawa, Y Maeno
Oxygen hole state in A-site ordered perovskite ACu3Ru 4O12 (A = Na, Ca, and La) probed by resonant X-ray emission spectroscopy Journal Article
In: Journal of the Physical Society of Japan, vol. 82, no. 2, 2013.
@article{Mizumaki2013,
title = {Oxygen hole state in A-site ordered perovskite ACu3Ru 4O12 (A = Na, Ca, and La) probed by resonant X-ray emission spectroscopy},
author = {M Mizumaki and T Mizokawa and A Agui and S Tanaka and H Takatsu and S Yonezawa and Y Maeno},
doi = {10.7566/JPSJ.82.024709},
year = {2013},
date = {2013-01-01},
journal = {Journal of the Physical Society of Japan},
volume = {82},
number = {2},
abstract = {In contrast to ordinary perovskites ABO3, A-site ordered perovskites AA′3B4O12 include transition metals in both A′ and B sites. The A′-O, B-O, and A′-B interactions in A-site ordered perovskites give rise to various physical properties. In this study, we report the O 1s and Cu 2p x-ray absorption spectroscopy (XAS) and resonant x-ray emission spectroscopy (RXES) study on the A-site ordered perovskite ACu3Ru4O12 (A = Na, Ca, and La). Hartree-Fock calculation and cluster model calculation were carried out to analyze O 1s and Cu 2p XAS spectra. The O 1s RXES spectra indicate that the number of O 2p holes increases in going from La to Ca to Na. In addition, the Cu 2p RXES spectra reveal that the charge-transfer (CT) energy decreases in going from La to Ca to Na. The decrease of CT is consistent with our calculations and suggest an increase of the O 2p holes in the ground state. The substitution of the A site ion changes not only the carrier concentration in the Ru 4d and Cu 3d bands but also the O 2p to Cu 3d CT energy. Copyright © 2013 The Physical Society of Japan.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In contrast to ordinary perovskites ABO3, A-site ordered perovskites AA′3B4O12 include transition metals in both A′ and B sites. The A′-O, B-O, and A′-B interactions in A-site ordered perovskites give rise to various physical properties. In this study, we report the O 1s and Cu 2p x-ray absorption spectroscopy (XAS) and resonant x-ray emission spectroscopy (RXES) study on the A-site ordered perovskite ACu3Ru4O12 (A = Na, Ca, and La). Hartree-Fock calculation and cluster model calculation were carried out to analyze O 1s and Cu 2p XAS spectra. The O 1s RXES spectra indicate that the number of O 2p holes increases in going from La to Ca to Na. In addition, the Cu 2p RXES spectra reveal that the charge-transfer (CT) energy decreases in going from La to Ca to Na. The decrease of CT is consistent with our calculations and suggest an increase of the O 2p holes in the ground state. The substitution of the A site ion changes not only the carrier concentration in the Ru 4d and Cu 3d bands but also the O 2p to Cu 3d CT energy. Copyright © 2013 The Physical Society of Japan.
738.
S Yonezawa, Y Maeno, D Jérome
vol. 449, no. 1, 2013.
@conference{Yonezawa2013c,
title = {Extended analysis of the field-angle-dependent heat capacity of (TMTSF)2ClO4 toward identification of the superconducting gap structure},
author = {S Yonezawa and Y Maeno and D Jérome},
doi = {10.1088/1742-6596/449/1/012032},
year = {2013},
date = {2013-01-01},
journal = {Journal of Physics: Conference Series},
volume = {449},
number = {1},
abstract = {In this paper, we present detailed analyses of the field-angle dependence of the heat capacity of the quasi-one-dimensional superconductor (TMTSF)2ClO4 with various models of superconducting gap structure. We clarify that the superconducting gap structure with line nodes at ky ±0.25b* is the only structure that is consistent with our experiment, irrespective of the value of the anion gap. The observed field-angle dependence of the heat capacity indicates that two of the four nodes mainly contribute to the quasiparticle excitation. © Published under licence by IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
In this paper, we present detailed analyses of the field-angle dependence of the heat capacity of the quasi-one-dimensional superconductor (TMTSF)2ClO4 with various models of superconducting gap structure. We clarify that the superconducting gap structure with line nodes at ky ±0.25b* is the only structure that is consistent with our experiment, irrespective of the value of the anion gap. The observed field-angle dependence of the heat capacity indicates that two of the four nodes mainly contribute to the quasiparticle excitation. © Published under licence by IOP Publishing Ltd.
737.
T Mito, H Hara, T Ishida, K Nakagawara, T Koyama, K Ueda, T Kohara, K Ishida, K Matsubayashi, Y Saiga, Y Uwatoko
Microscopic evidence of a crossover to a low-temperature intermediate valence state in YbCo2Zn20 Journal Article
In: Journal of the Physical Society of Japan, vol. 82, no. 10, 2013.
@article{Mito2013,
title = {Microscopic evidence of a crossover to a low-temperature intermediate valence state in YbCo2Zn20},
author = {T Mito and H Hara and T Ishida and K Nakagawara and T Koyama and K Ueda and T Kohara and K Ishida and K Matsubayashi and Y Saiga and Y Uwatoko},
doi = {10.7566/JPSJ.82.103704},
year = {2013},
date = {2013-01-01},
journal = {Journal of the Physical Society of Japan},
volume = {82},
number = {10},
abstract = {The low-temperature properties of YbCo2Zn20, which shows a giant specific heat at low temperatures, have been studied by the 59Co-nuclear quadrupole resonance (NQR) technique. The measurement of spin lattice relaxation rate reveals that Yb 4f-electrons unusually persist in a well-localized regime down to at least 0.3K without ordering magnetically. With further lowering temperature, NQR frequency decreases below 0.2K reflecting the lowtemperature Fermi liquid state, even suggesting a crossover to an intermediate valence state in close proximity to the localized-delocalzied transition. We also compare the observed unique properties of YbCo 2Zn20 with those of YbRh2Si2, which shows antiferromagnetic ordering at extremely low temperature. © 2013 The Physical Society of Japan.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The low-temperature properties of YbCo2Zn20, which shows a giant specific heat at low temperatures, have been studied by the 59Co-nuclear quadrupole resonance (NQR) technique. The measurement of spin lattice relaxation rate reveals that Yb 4f-electrons unusually persist in a well-localized regime down to at least 0.3K without ordering magnetically. With further lowering temperature, NQR frequency decreases below 0.2K reflecting the lowtemperature Fermi liquid state, even suggesting a crossover to an intermediate valence state in close proximity to the localized-delocalzied transition. We also compare the observed unique properties of YbCo 2Zn20 with those of YbRh2Si2, which shows antiferromagnetic ordering at extremely low temperature. © 2013 The Physical Society of Japan.
736.
T Hattori, K Karube, Y Ihara, K Ishida, K Deguchi, N K Sato, T Yamamura
Spin susceptibility in the superconducting state of the ferromagnetic superconductor UCoGe Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 88, no. 8, 2013.
@article{Hattori2013,
title = {Spin susceptibility in the superconducting state of the ferromagnetic superconductor UCoGe},
author = {T Hattori and K Karube and Y Ihara and K Ishida and K Deguchi and N K Sato and T Yamamura},
doi = {10.1103/PhysRevB.88.085127},
year = {2013},
date = {2013-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {88},
number = {8},
abstract = {In order to determine the superconducting paring state in the ferromagnetic superconductor UCoGe, the 59Co NMR Knight shift, which is directly related to the microscopic spin susceptibility, was measured in the superconducting state under magnetic fields perpendicular to the spontaneous magnetization axis 59Ka,b. 59Ka,b shows to be almost constant, but does not decrease below a superconducting transition. These behaviors as well as the invariance of the internal field at the Co site in the superconducting state exclude the spin-singlet pairing, and can be interpreted with the equal-spin pairing state with a large exchange field along the c axis, which was studied by Mineev. © 2013 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In order to determine the superconducting paring state in the ferromagnetic superconductor UCoGe, the 59Co NMR Knight shift, which is directly related to the microscopic spin susceptibility, was measured in the superconducting state under magnetic fields perpendicular to the spontaneous magnetization axis 59Ka,b. 59Ka,b shows to be almost constant, but does not decrease below a superconducting transition. These behaviors as well as the invariance of the internal field at the Co site in the superconducting state exclude the spin-singlet pairing, and can be interpreted with the equal-spin pairing state with a large exchange field along the c axis, which was studied by Mineev. © 2013 American Physical Society.
735.
K Karube, T Hattori, K Ishida, N Tamura, K Deguchi, N K Sato
Spin-density-wave-type ordering of LaCoGe revealed by 59Co-and 139La-nuclear magnetic resonance measurements Journal Article
In: Journal of the Physical Society of Japan, vol. 82, no. 8, 2013.
@article{Karube2013,
title = {Spin-density-wave-type ordering of LaCoGe revealed by 59Co-and 139La-nuclear magnetic resonance measurements},
author = {K Karube and T Hattori and K Ishida and N Tamura and K Deguchi and N K Sato},
doi = {10.7566/JPSJ.82.083712},
year = {2013},
date = {2013-01-01},
journal = {Journal of the Physical Society of Japan},
volume = {82},
number = {8},
abstract = {The low-temperature magnetic properties of LaCoGe with the tetragonal CeFeSi-type structure were investigated by 59Co- and 139La-nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements. The nuclear spin-lattice relaxation rate divided by the temperature},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The low-temperature magnetic properties of LaCoGe with the tetragonal CeFeSi-type structure were investigated by 59Co- and 139La-nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements. The nuclear spin-lattice relaxation rate divided by the temperature
734.
Y Nakai, T Iye, S Kitagawa, K Ishida, S Kasahara, T Shibauchi, Y Matsuda, H Ikeda, T Terashima
Normal-state spin dynamics in the iron-pnictide superconductors BaFe 2(As1-xPx)2 and Ba(Fe 1-xCox)2As2 probed with NMR measurements Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 87, no. 17, 2013.
@article{Nakai2013,
title = {Normal-state spin dynamics in the iron-pnictide superconductors BaFe 2(As1-xPx)2 and Ba(Fe 1-xCox)2As2 probed with NMR measurements},
author = {Y Nakai and T Iye and S Kitagawa and K Ishida and S Kasahara and T Shibauchi and Y Matsuda and H Ikeda and T Terashima},
doi = {10.1103/PhysRevB.87.174507},
year = {2013},
date = {2013-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {87},
number = {17},
abstract = {The NMR results in iron pnictides BaFe2(As1-xP x)2 and Ba(Fe1-xCox) 2As2 are analyzed based on the self-consistent renormalization (SCR) spin-fluctuation theory. The temperature dependence of the NMR relaxation rate T1-1 as well as the electrical resistivity is well reproduced by a SCR model where two-dimensional antiferromagnetic (AF) spin fluctuations are dominant. The successful description of the crossover feature from non-Fermi-liquid to Fermi-liquid behavior strongly suggests that low-lying spin fluctuations in BaFe2(As1-xPx)2 and Ba(Fe1-xCox)2As2 possess an itinerant AF nature, and that chemical substitution in the two compounds tunes the distance of these systems to an AF quantum critical point. The close relationship between spin fluctuations and superconductivity is discussed compared with the other unconventional superconductors, cuprate and heavy fermion superconductors. In addition, it is suggested that magnetism and lattice instability in these pnictides are strongly linked via orbital degrees of freedom. © 2013 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The NMR results in iron pnictides BaFe2(As1-xP x)2 and Ba(Fe1-xCox) 2As2 are analyzed based on the self-consistent renormalization (SCR) spin-fluctuation theory. The temperature dependence of the NMR relaxation rate T1-1 as well as the electrical resistivity is well reproduced by a SCR model where two-dimensional antiferromagnetic (AF) spin fluctuations are dominant. The successful description of the crossover feature from non-Fermi-liquid to Fermi-liquid behavior strongly suggests that low-lying spin fluctuations in BaFe2(As1-xPx)2 and Ba(Fe1-xCox)2As2 possess an itinerant AF nature, and that chemical substitution in the two compounds tunes the distance of these systems to an AF quantum critical point. The close relationship between spin fluctuations and superconductivity is discussed compared with the other unconventional superconductors, cuprate and heavy fermion superconductors. In addition, it is suggested that magnetism and lattice instability in these pnictides are strongly linked via orbital degrees of freedom. © 2013 American Physical Society.
733.
S Kitagawa, K Ishida, T Nakamura, M Matoba, Y Kamihara
Ferromagnetic quantum critical point induced by tuning the magnetic dimensionality of the heavy-fermion iron oxypnictide Ce(Ru1-xFe x)PO Journal Article
In: Journal of the Physical Society of Japan, vol. 82, no. 3, 2013.
@article{Kitagawa2013,
title = {Ferromagnetic quantum critical point induced by tuning the magnetic dimensionality of the heavy-fermion iron oxypnictide Ce(Ru1-xFe x)PO},
author = {S Kitagawa and K Ishida and T Nakamura and M Matoba and Y Kamihara},
doi = {10.7566/JPSJ.82.033704},
year = {2013},
date = {2013-01-01},
journal = {Journal of the Physical Society of Japan},
volume = {82},
number = {3},
abstract = {We have performed 31P-NMR measurements of the c-axis-aligned poly-crystal Ce(Ru1-xFex)PO with a twodimensional layered structure in order to understand the origin of TCurie suppression by Fe substitution. The variation in the magnetic-fluctuation character with respect to x is investigated from the in-plane and out-of-plane fluctuations and the relationship between the static spin susceptibility and the in-plane fluctuation. It was found that three-dimensional ferromagnetic (FM) correlations are dominant and give rise to the FM ordering in CeRuPO. The out-of plane fluctuations are significantly suppressed with increasing x, and it was revealed that the FM fluctuations become two dimensional near a FM quantum critical point (QCP). Our NMR results strongly suggest that a unique FM QCP in Ce(Ru 1-xFex)PO is induced by the suppression of the magnetic correlations along the c-axis, which is a different mechanism from that presumed in heavy-fermion compounds. © 2013 The Physical Society of Japan.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We have performed 31P-NMR measurements of the c-axis-aligned poly-crystal Ce(Ru1-xFex)PO with a twodimensional layered structure in order to understand the origin of TCurie suppression by Fe substitution. The variation in the magnetic-fluctuation character with respect to x is investigated from the in-plane and out-of-plane fluctuations and the relationship between the static spin susceptibility and the in-plane fluctuation. It was found that three-dimensional ferromagnetic (FM) correlations are dominant and give rise to the FM ordering in CeRuPO. The out-of plane fluctuations are significantly suppressed with increasing x, and it was revealed that the FM fluctuations become two dimensional near a FM quantum critical point (QCP). Our NMR results strongly suggest that a unique FM QCP in Ce(Ru 1-xFex)PO is induced by the suppression of the magnetic correlations along the c-axis, which is a different mechanism from that presumed in heavy-fermion compounds. © 2013 The Physical Society of Japan.
732.
S Kitagawa, K Ishida, K Nakano, T Yajima, H Kageyama
S-wave superconductivity in superconducting BaTi2Sb2O revealed by 121/123Sb-NMR/nuclear quadrupole resonance measurements Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 87, no. 6, 2013.
@article{Kitagawa2013b,
title = {S-wave superconductivity in superconducting BaTi2Sb2O revealed by 121/123Sb-NMR/nuclear quadrupole resonance measurements},
author = {S Kitagawa and K Ishida and K Nakano and T Yajima and H Kageyama},
doi = {10.1103/PhysRevB.87.060510},
year = {2013},
date = {2013-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {87},
number = {6},
abstract = {We report the 121/123Sb-NMR/nuclear quadrupole resonance (NQR) measurements on the superconductor BaTi2Sb2O with a two-dimensional Ti2O square-net layer formed with Ti3+ (3d1). NQR measurements revealed that the in-plane four-fold symmetry is broken at the Sb site below TA∼40 K, without an internal field appearing at the Sb site. These exclude a spin-density wave (SDW)/ charge density wave (CDW) ordering with incommensurate correlations, but can be understood with the commensurate CDW ordering at TA. The spin-lattice relaxation rate 1/T1, measured at the four-fold symmetry breaking site, decreases below superconducting (SC) transition temperature Tc, indicative of the microscopic coexistence of superconductivity and the CDW/SDW phase below TA. Furthermore, 1/T1 of 121Sb-NQR shows a coherence peak just below Tc and decreases exponentially at low temperatures. These results are in sharp contrast with those in cuprate and iron-based superconductors, and strongly suggest that its SC symmetry is classified to an ordinary s-wave state. © 2013 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report the 121/123Sb-NMR/nuclear quadrupole resonance (NQR) measurements on the superconductor BaTi2Sb2O with a two-dimensional Ti2O square-net layer formed with Ti3+ (3d1). NQR measurements revealed that the in-plane four-fold symmetry is broken at the Sb site below TA∼40 K, without an internal field appearing at the Sb site. These exclude a spin-density wave (SDW)/ charge density wave (CDW) ordering with incommensurate correlations, but can be understood with the commensurate CDW ordering at TA. The spin-lattice relaxation rate 1/T1, measured at the four-fold symmetry breaking site, decreases below superconducting (SC) transition temperature Tc, indicative of the microscopic coexistence of superconductivity and the CDW/SDW phase below TA. Furthermore, 1/T1 of 121Sb-NQR shows a coherence peak just below Tc and decreases exponentially at low temperatures. These results are in sharp contrast with those in cuprate and iron-based superconductors, and strongly suggest that its SC symmetry is classified to an ordinary s-wave state. © 2013 American Physical Society.
731.
Y Tada, S Fujimoto, N Kawakami, T Hattori, Y Ihara, K Ishida, K Deguchi, N K Sato, I Satoh
vol. 449, no. 1, 2013.
@conference{Tada2013,
title = {Spin-triplet superconductivity induced by longitudinal ferromagnetic fluctuations in UCoGe: Theoretical aspect},
author = {Y Tada and S Fujimoto and N Kawakami and T Hattori and Y Ihara and K Ishida and K Deguchi and N K Sato and I Satoh},
doi = {10.1088/1742-6596/449/1/012029},
year = {2013},
date = {2013-01-01},
journal = {Journal of Physics: Conference Series},
volume = {449},
number = {1},
abstract = {Identification of pairing mechanisms leading to the unconventional superconductivity realized in copper-oxide, heavy-fermions, and organic compounds is one of the most challenging issues in condensed-matter physics. Clear evidence for an electron-phonon mechanism in conventional superconductors is seen by the isotope effect on the superconducting transition temperatures TSC, since isotopic substitution varies the phonon frequency without affecting the electronic states. In unconventional superconductors, magnetic fluctuations have been proposed to mediate superconductivity, and considerable efforts have been made to unravel relationships between normal-state magnetic fluctuations and superconductivity. Here, we show that characteristic experimental results on the ferromagnetic (FM) superconductor UCoGe (TCurie ∼ 2.5 K and TSC ∼ 0.6 K) can be understood consistently within a scenario of the spin-triplet superconductivity induced by FM spin fluctuations. Temperature and angle dependencies of the upper critical magnetic field of the superconductivity (Hc2) are calculated on the basis of the above scenario by solving the Eliashberg equation. Calculated Hc2 well agrees with the characteristic experimental results observed in UCoGe. This is a first example that FM fluctuations are shown to be a pairing glue of superconductivity. © Published under licence by IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
Identification of pairing mechanisms leading to the unconventional superconductivity realized in copper-oxide, heavy-fermions, and organic compounds is one of the most challenging issues in condensed-matter physics. Clear evidence for an electron-phonon mechanism in conventional superconductors is seen by the isotope effect on the superconducting transition temperatures TSC, since isotopic substitution varies the phonon frequency without affecting the electronic states. In unconventional superconductors, magnetic fluctuations have been proposed to mediate superconductivity, and considerable efforts have been made to unravel relationships between normal-state magnetic fluctuations and superconductivity. Here, we show that characteristic experimental results on the ferromagnetic (FM) superconductor UCoGe (TCurie ∼ 2.5 K and TSC ∼ 0.6 K) can be understood consistently within a scenario of the spin-triplet superconductivity induced by FM spin fluctuations. Temperature and angle dependencies of the upper critical magnetic field of the superconductivity (Hc2) are calculated on the basis of the above scenario by solving the Eliashberg equation. Calculated Hc2 well agrees with the characteristic experimental results observed in UCoGe. This is a first example that FM fluctuations are shown to be a pairing glue of superconductivity. © Published under licence by IOP Publishing Ltd.
2012
730.
Y Kawashima, G Eguchi, S Yonezawa, Y Maeno
Superconductivity in La3Pt4 Journal Article
In: Journal of the Physical Society of Japan, vol. 81, no. 12, 2012.
@article{Kawashima2012,
title = {Superconductivity in La3Pt4},
author = {Y Kawashima and G Eguchi and S Yonezawa and Y Maeno},
doi = {10.1143/JPSJ.81.125001},
year = {2012},
date = {2012-01-01},
journal = {Journal of the Physical Society of Japan},
volume = {81},
number = {12},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
729.
G Eguchi, H Wadati, T Sugiyama, E Ikenaga, S Yonezawa, Y Maeno
Large spin-orbit splitting and weakly anisotropic superconductivity revealed with single-crystalline noncentrosymmetric CaIrSi 3 Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 86, no. 18, 2012.
@article{Eguchi2012,
title = {Large spin-orbit splitting and weakly anisotropic superconductivity revealed with single-crystalline noncentrosymmetric CaIrSi 3},
author = {G Eguchi and H Wadati and T Sugiyama and E Ikenaga and S Yonezawa and Y Maeno},
doi = {10.1103/PhysRevB.86.184510},
year = {2012},
date = {2012-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {86},
number = {18},
abstract = {We report normal and superconducting properties of the Rashba-type noncentrosymmetric compound CaIrSi 3 using single crystalline samples with nearly 100% superconducting volume fraction. The electronic density of states revealed by the hard x-ray photoemission spectroscopy can be well explained by the relativistic first-principles band calculation. This indicates that strong spin-orbit interaction indeed affects the electronic states of this compound. The obtained H-T phase diagram exhibits only approximately 10% anisotropy, indicating that the superconducting properties are almost three dimensional. Nevertheless, strongly anisotropic vortex pinning is observed. © 2012 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report normal and superconducting properties of the Rashba-type noncentrosymmetric compound CaIrSi 3 using single crystalline samples with nearly 100% superconducting volume fraction. The electronic density of states revealed by the hard x-ray photoemission spectroscopy can be well explained by the relativistic first-principles band calculation. This indicates that strong spin-orbit interaction indeed affects the electronic states of this compound. The obtained H-T phase diagram exhibits only approximately 10% anisotropy, indicating that the superconducting properties are almost three dimensional. Nevertheless, strongly anisotropic vortex pinning is observed. © 2012 American Physical Society.
728.
K Saitoh, S Kashiwaya, H Kashiwaya, M Koyanagi, Y Mawatari, Y Tanaka, Y Maeno
High-supercurrent-density contacts and josephson effect of strontium ruthenate Journal Article
In: Applied Physics Express, vol. 5, no. 11, 2012.
@article{Saitoh2012,
title = {High-supercurrent-density contacts and josephson effect of strontium ruthenate},
author = {K Saitoh and S Kashiwaya and H Kashiwaya and M Koyanagi and Y Mawatari and Y Tanaka and Y Maeno},
doi = {10.1143/APEX.5.113101},
year = {2012},
date = {2012-01-01},
journal = {Applied Physics Express},
volume = {5},
number = {11},
abstract = {We have developed a process of fabricating high-supercurrent-density contacts to Sr2RuO4 as a key technology for the development of topological quantum computing. To minimize degradation, the niobium contacts were formed on crushed surfaces of Sr2RuO 4 crystals by an in situ process. A critical supercurrent density as high as 107 A/m2 was achieved, a value two to three orders of magnitude greater than those reported previously. However, the unexpectedly small magnitude of the product of the critical current and the normal resistance indicates the existence of a fundamental limitation arising from Josephson coupling between spin-singlet and spin-triplet superconductivities. © 2012 The Japan Society of Applied Physics.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We have developed a process of fabricating high-supercurrent-density contacts to Sr2RuO4 as a key technology for the development of topological quantum computing. To minimize degradation, the niobium contacts were formed on crushed surfaces of Sr2RuO 4 crystals by an in situ process. A critical supercurrent density as high as 107 A/m2 was achieved, a value two to three orders of magnitude greater than those reported previously. However, the unexpectedly small magnitude of the product of the critical current and the normal resistance indicates the existence of a fundamental limitation arising from Josephson coupling between spin-singlet and spin-triplet superconductivities. © 2012 The Japan Society of Applied Physics.
727.
C W Hicks, A S Gibbs, A P Mackenzie, H Takatsu, Y Maeno, E A Yelland
Quantum oscillations and high carrier mobility in the delafossite PdCoO 2 Journal Article
In: Physical Review Letters, vol. 109, no. 11, 2012.
@article{Hicks2012,
title = {Quantum oscillations and high carrier mobility in the delafossite PdCoO 2},
author = {C W Hicks and A S Gibbs and A P Mackenzie and H Takatsu and Y Maeno and E A Yelland},
doi = {10.1103/PhysRevLett.109.116401},
year = {2012},
date = {2012-01-01},
journal = {Physical Review Letters},
volume = {109},
number = {11},
abstract = {We present de Haas-van Alphen and resistivity data on single crystals of the delafossite PdCoO 2. At 295 K we measure an in-plane resistivity of 2.6μΩcm, making PdCoO 2 the most conductive oxide known. The low-temperature in-plane resistivity has an activated rather than the usual T5 temperature dependence, suggesting a gapping of effective scattering that is consistent with phonon drag. Below 10 K, the transport mean free path is ∼20μm, approximately 105 lattice spacings and an astoundingly high value for flux-grown crystals. We discuss the origin of these properties in light of our data. © 2012 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We present de Haas-van Alphen and resistivity data on single crystals of the delafossite PdCoO 2. At 295 K we measure an in-plane resistivity of 2.6μΩcm, making PdCoO 2 the most conductive oxide known. The low-temperature in-plane resistivity has an activated rather than the usual T5 temperature dependence, suggesting a gapping of effective scattering that is consistent with phonon drag. Below 10 K, the transport mean free path is ∼20μm, approximately 105 lattice spacings and an astoundingly high value for flux-grown crystals. We discuss the origin of these properties in light of our data. © 2012 American Physical Society.
726.
G Eguchi, F Kneidinger, L Salamakha, S Yonezawa, Y Maeno, E Bauer
Pressure study of the noncentrosymmetric 5d-electron superconductors CaMSi 3 (M = Ir, Pt) Journal Article
In: Journal of the Physical Society of Japan, vol. 81, no. 7, 2012.
@article{Eguchi2012b,
title = {Pressure study of the noncentrosymmetric 5d-electron superconductors CaMSi 3 (M = Ir, Pt)},
author = {G Eguchi and F Kneidinger and L Salamakha and S Yonezawa and Y Maeno and E Bauer},
doi = {10.1143/JPSJ.81.074711},
year = {2012},
date = {2012-01-01},
journal = {Journal of the Physical Society of Japan},
volume = {81},
number = {7},
abstract = {We report a hydrostatic pressure study on the Rashba-type noncentrosymmetric superconductors CaMSi 3 (M = Ir, Pt). The temperature dependence of the resistivity of both compounds is well described by the conventional Bloch-Grüneisen formalism at each pressure. This fact suggests that electron-phonon scattering is dominant in these compounds. The superconducting critical temperature T c decreases with pressure above 0.41 to 2 GPa at a rate of ∼0.2 K/GPa for both compounds. This T c behavior can be explained with a modest decrease in the density of states based on the conventional BCS theory. © 2012 The Physical Society of Japan.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report a hydrostatic pressure study on the Rashba-type noncentrosymmetric superconductors CaMSi 3 (M = Ir, Pt). The temperature dependence of the resistivity of both compounds is well described by the conventional Bloch-Grüneisen formalism at each pressure. This fact suggests that electron-phonon scattering is dominant in these compounds. The superconducting critical temperature T c decreases with pressure above 0.41 to 2 GPa at a rate of ∼0.2 K/GPa for both compounds. This T c behavior can be explained with a modest decrease in the density of states based on the conventional BCS theory. © 2012 The Physical Society of Japan.
725.
T Nakamura, T Sumi, S Yonezawa, T Terashima, M Sigrist, H Kaneyasu, Y Maeno
Essential configuration of Pb/Ru/ Sr 2RuO 4 junctions exhibiting anomalous superconducting interference Journal Article
In: Journal of the Physical Society of Japan, vol. 81, no. 6, 2012.
@article{Nakamura2012,
title = {Essential configuration of Pb/Ru/ Sr 2RuO 4 junctions exhibiting anomalous superconducting interference},
author = {T Nakamura and T Sumi and S Yonezawa and T Terashima and M Sigrist and H Kaneyasu and Y Maeno},
doi = {10.1143/JPSJ.81.064708},
year = {2012},
date = {2012-01-01},
journal = {Journal of the Physical Society of Japan},
volume = {81},
number = {6},
abstract = {We fabricate several unconventional proximity junctions of Sr2RuO4 and Pb with the precise control of the junction configurations achieved using a focused-ion beam. We observe a sharp drop of the critical current just below the transition temperature of the bulk Sr 2RuO 4 irrespective of Ru arrangement in the junctions. We further demonstrate that the essential configuration giving rise to such an anomalous critical current is a single Pb/Ru/ Sr 2RuO 4 junction. The anomalous suppression is ascribable to a topological transition of the superconducting order parameter of Sr 2RuO 4. © 2012 The Physical Society of Japan.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We fabricate several unconventional proximity junctions of Sr2RuO4 and Pb with the precise control of the junction configurations achieved using a focused-ion beam. We observe a sharp drop of the critical current just below the transition temperature of the bulk Sr 2RuO 4 irrespective of Ru arrangement in the junctions. We further demonstrate that the essential configuration giving rise to such an anomalous critical current is a single Pb/Ru/ Sr 2RuO 4 junction. The anomalous suppression is ascribable to a topological transition of the superconducting order parameter of Sr 2RuO 4. © 2012 The Physical Society of Japan.
724.
G Sala, C Castelnovo, R Moessner, S L Sondhi, K Kitagawa, M Takigawa, R Higashinaka, Y Maeno
Magnetic Coulomb fields of monopoles in spin ice and their signatures in the internal field distribution Journal Article
In: Physical Review Letters, vol. 108, no. 21, 2012.
@article{Sala2012,
title = {Magnetic Coulomb fields of monopoles in spin ice and their signatures in the internal field distribution},
author = {G Sala and C Castelnovo and R Moessner and S L Sondhi and K Kitagawa and M Takigawa and R Higashinaka and Y Maeno},
doi = {10.1103/PhysRevLett.108.217203},
year = {2012},
date = {2012-01-01},
journal = {Physical Review Letters},
volume = {108},
number = {21},
abstract = {Fractionalization-the breaking up of an apparently indivisible microscopic degree of freedom-is one of the most counterintuitive phenomena in many-body physics. Here we study its most fundamental manifestation in spin ice, the only known fractionalized magnetic compound in 3D: we directly visualize the 1/r2 magnetic Coulomb field of monopoles that emerge as the atomic magnetic dipoles fractionalize. We analyze the internal magnetic field distribution, relevant for local experimental probes. In particular, we present new zero-field NMR measurements that exhibit excellent agreement with the calculated line shapes, noting that this experimental technique can in principle measure directly the monopole density in spin ice. The distribution of field strengths is captured by a simple analytical form that exhibits a low density of low-field sites-in apparent disagreement with reported muon spin rotation results. Counterintuitively, the density of low-field locations decreases as the local ferromagnetic correlations imposed by the ice rules weaken. © 2012 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Fractionalization-the breaking up of an apparently indivisible microscopic degree of freedom-is one of the most counterintuitive phenomena in many-body physics. Here we study its most fundamental manifestation in spin ice, the only known fractionalized magnetic compound in 3D: we directly visualize the 1/r2 magnetic Coulomb field of monopoles that emerge as the atomic magnetic dipoles fractionalize. We analyze the internal magnetic field distribution, relevant for local experimental probes. In particular, we present new zero-field NMR measurements that exhibit excellent agreement with the calculated line shapes, noting that this experimental technique can in principle measure directly the monopole density in spin ice. The distribution of field strengths is captured by a simple analytical form that exhibits a low density of low-field sites-in apparent disagreement with reported muon spin rotation results. Counterintuitively, the density of low-field locations decreases as the local ferromagnetic correlations imposed by the ice rules weaken. © 2012 American Physical Society.
723.
T Shiroka, R Fittipaldi, M Cuoco, R De Renzi, Y Maeno, R J Lycett, S Ramos, E M Forgan, C Baines, A Rost, V Granata, A Vecchione
μsR studies of superconductivity in eutectically grown mixed ruthenates Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 85, no. 13, 2012.
@article{Shiroka2012,
title = {μsR studies of superconductivity in eutectically grown mixed ruthenates},
author = {T Shiroka and R Fittipaldi and M Cuoco and R De Renzi and Y Maeno and R J Lycett and S Ramos and E M Forgan and C Baines and A Rost and V Granata and A Vecchione},
doi = {10.1103/PhysRevB.85.134527},
year = {2012},
date = {2012-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {85},
number = {13},
abstract = {The low-temperature magnetic behavior of the double-layered ruthenate Sr 3Ru 2O 7, as grown from a eutectic Sr 2RuO 4-Sr 3Ru 2O 7 system, was investigated via zero- and transverse-field muon-spin rotation. The gradual increase of the muon relaxation rate observed below 2.5 K, even in the absence of applied magnetic fields, indicates the occurrence of a spontaneous breaking of time-reversal symmetry. The onset of the latter at a temperature above 1.5 K, the T c of the single phase Sr 2RuO 4, provides evidence about an unconventional superconducting state in the eutectic phase, which most likely takes place at the interface between the Sr 2RuO 4 and Sr 3Ru 2O 7 domains, or even inside the Sr 3Ru 2O 7 phase. We show that the superconducting state manifests a two-component behavior in the transverse-field response with change-over at about T=2.5 K and T=1.5 K. The comparison with zero-field μSR data in the Ru-Sr 2RuO 4 eutectic system rules out the possibility of spurious effects due to embedded Ru islands. © 2012 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The low-temperature magnetic behavior of the double-layered ruthenate Sr 3Ru 2O 7, as grown from a eutectic Sr 2RuO 4-Sr 3Ru 2O 7 system, was investigated via zero- and transverse-field muon-spin rotation. The gradual increase of the muon relaxation rate observed below 2.5 K, even in the absence of applied magnetic fields, indicates the occurrence of a spontaneous breaking of time-reversal symmetry. The onset of the latter at a temperature above 1.5 K, the T c of the single phase Sr 2RuO 4, provides evidence about an unconventional superconducting state in the eutectic phase, which most likely takes place at the interface between the Sr 2RuO 4 and Sr 3Ru 2O 7 domains, or even inside the Sr 3Ru 2O 7 phase. We show that the superconducting state manifests a two-component behavior in the transverse-field response with change-over at about T=2.5 K and T=1.5 K. The comparison with zero-field μSR data in the Ru-Sr 2RuO 4 eutectic system rules out the possibility of spurious effects due to embedded Ru islands. © 2012 American Physical Society.
722.
S Yonezawa, Y Maeno, K Bechgaard, D Jérome
Nodal superconducting order parameter and thermodynamic phase diagram of (TMTSF) 2ClO 4 Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 85, no. 14, 2012.
@article{Yonezawa2012,
title = {Nodal superconducting order parameter and thermodynamic phase diagram of (TMTSF) 2ClO 4},
author = {S Yonezawa and Y Maeno and K Bechgaard and D Jérome},
doi = {10.1103/PhysRevB.85.140502},
year = {2012},
date = {2012-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {85},
number = {14},
abstract = {The organic materials (TMTSF) 2X are unique unconventional superconductors with archetypal quasi-one-dimensional (Q1D) electronic structures. Here, based on our comprehensive field-angle-resolved calorimetry of (TMTSF) 2ClO 4, we succeeded in mapping the nodal gap structure by discriminating between the Fermi wave vectors and Fermi velocities. In addition, the thermodynamic phase diagrams of (TMTSF) 2ClO 4 for all principal field directions are obtained. These findings, providing strong evidence of nodal spin-singlet superconductivity, serves as solid bases for the further elucidation of anomalous superconducting phenomena in (TMTSF) 2X. © 2012 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The organic materials (TMTSF) 2X are unique unconventional superconductors with archetypal quasi-one-dimensional (Q1D) electronic structures. Here, based on our comprehensive field-angle-resolved calorimetry of (TMTSF) 2ClO 4, we succeeded in mapping the nodal gap structure by discriminating between the Fermi wave vectors and Fermi velocities. In addition, the thermodynamic phase diagrams of (TMTSF) 2ClO 4 for all principal field directions are obtained. These findings, providing strong evidence of nodal spin-singlet superconductivity, serves as solid bases for the further elucidation of anomalous superconducting phenomena in (TMTSF) 2X. © 2012 American Physical Society.
721.
H Taniguchi, S Kittaka, S Yonezawa, H Yaguchi, Y Maeno
vol. 391, no. 1, 2012.
@conference{Taniguchi2012,
title = {Field-temperature phase diagram of superconductivity in Sr 2RuO4-Ru under out-of-plane uniaxial pressure},
author = {H Taniguchi and S Kittaka and S Yonezawa and H Yaguchi and Y Maeno},
doi = {10.1088/1742-6596/391/1/012108},
year = {2012},
date = {2012-01-01},
journal = {Journal of Physics: Conference Series},
volume = {391},
number = {1},
abstract = {One of the interesting issues on the spin-triplet superconductor Sr2RuO4 (Tc 1.5 K) is the origin of the Tc enhancement up to about 3 K in the eutectic system Sr2RuO4-Ru. We have recently revealed a striking fact that Tc of pure Sr2RuO4 is also enhanced up to 3.2 K by uniaxial pressure along the c axis (P||c). When P||c is applied to Sr2RuO4-Ru, there is a crossover at P *||c ∼ 0.4 GPa from behavior attributable to interfacial superconductivity (SC) to behavior similar to that in pure Sr2RuO4 under P||c. We focus on the field-temperature phase diagrams of Sr2RuO4-Ru above and below P*||c. We revealed that the H-T curves of Sr2RuO4-Ru both above and below P*||c are concave-up. This fact suggests that the P||c-originated SC above P*||c as well as the interfacial SC below P*||c are granular-like. We also found that the H-T curves of these SCs do not scale with Tc's, which is possibly related to a difference in the spatial distribution of superconducting regions. © Published under licence by IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
One of the interesting issues on the spin-triplet superconductor Sr2RuO4 (Tc 1.5 K) is the origin of the Tc enhancement up to about 3 K in the eutectic system Sr2RuO4-Ru. We have recently revealed a striking fact that Tc of pure Sr2RuO4 is also enhanced up to 3.2 K by uniaxial pressure along the c axis (P||c). When P||c is applied to Sr2RuO4-Ru, there is a crossover at P *||c ∼ 0.4 GPa from behavior attributable to interfacial superconductivity (SC) to behavior similar to that in pure Sr2RuO4 under P||c. We focus on the field-temperature phase diagrams of Sr2RuO4-Ru above and below P*||c. We revealed that the H-T curves of Sr2RuO4-Ru both above and below P*||c are concave-up. This fact suggests that the P||c-originated SC above P*||c as well as the interfacial SC below P*||c are granular-like. We also found that the H-T curves of these SCs do not scale with Tc's, which is possibly related to a difference in the spatial distribution of superconducting regions. © Published under licence by IOP Publishing Ltd.
720.
Y Maeno, S Kittaka, T Nomura, S Yonezawa, K Ishida
Evaluation of spin-triplet superconductivity in Sr 2RuO 4 Journal Article
In: Journal of the Physical Society of Japan, vol. 81, no. 1, 2012.
@article{Maeno2012,
title = {Evaluation of spin-triplet superconductivity in Sr 2RuO 4},
author = {Y Maeno and S Kittaka and T Nomura and S Yonezawa and K Ishida},
doi = {10.1143/JPSJ.81.011009},
year = {2012},
date = {2012-01-01},
journal = {Journal of the Physical Society of Japan},
volume = {81},
number = {1},
abstract = {This review presents a summary and evaluations of the superconducting properties of the layered ruthenate Sr 2RuO 4 as they are known in the autumn of 2011. This paper appends the main progress that has been made since the preceding review by Mackenzie and Maeno was published in 2003. Here, special focus is placed on the critical evaluation of the spin-triplet, odd-parity pairing scenario applied to Sr 2RuO 4. After an introduction to superconductors with possible odd-parity pairing, accumulated evidence for the pairing symmetry of Sr 2RuO 4 is examined. Then, significant recent progress on the theoretical approaches to the superconducting pairing by Coulomb repulsion is reviewed. A section is devoted to some experimental properties of Sr 2RuO 4 that seem to defy simple explanations in terms of currently available spin-triplet scenario. The next section deals with some new developments using eutectic boundaries and micro-crystals, which reveals novel superconducting phenomena related to chiral edge states, odd-frequency pairing states, and half-fluxoid states. Some of these properties are intimately connected with the properties as a topological superconductor. The article concludes with a summary of knowledge emerged from the study of Sr 2RuO 4 that are now more widely applied to understand the physics of other unconventional superconductors, as well as with a brief discussion of relatively unexplored but promising areas of ongoing and future studies of Sr 2RuO 4. © 2012 The Physical Society of Japan.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This review presents a summary and evaluations of the superconducting properties of the layered ruthenate Sr 2RuO 4 as they are known in the autumn of 2011. This paper appends the main progress that has been made since the preceding review by Mackenzie and Maeno was published in 2003. Here, special focus is placed on the critical evaluation of the spin-triplet, odd-parity pairing scenario applied to Sr 2RuO 4. After an introduction to superconductors with possible odd-parity pairing, accumulated evidence for the pairing symmetry of Sr 2RuO 4 is examined. Then, significant recent progress on the theoretical approaches to the superconducting pairing by Coulomb repulsion is reviewed. A section is devoted to some experimental properties of Sr 2RuO 4 that seem to defy simple explanations in terms of currently available spin-triplet scenario. The next section deals with some new developments using eutectic boundaries and micro-crystals, which reveals novel superconducting phenomena related to chiral edge states, odd-frequency pairing states, and half-fluxoid states. Some of these properties are intimately connected with the properties as a topological superconductor. The article concludes with a summary of knowledge emerged from the study of Sr 2RuO 4 that are now more widely applied to understand the physics of other unconventional superconductors, as well as with a brief discussion of relatively unexplored but promising areas of ongoing and future studies of Sr 2RuO 4. © 2012 The Physical Society of Japan.
719.
R Ishikawa, H Taniguchi, S Kuan Goh, S Yonezawa, F Nakamura, Y Maeno
Control of the electronic states of Ca2RuO4 by uniaxial pressure Conference
vol. 400, no. PART 2, 2012.
@conference{Ishikawa2012,
title = {Control of the electronic states of Ca2RuO4 by uniaxial pressure},
author = {R Ishikawa and H Taniguchi and S Kuan Goh and S Yonezawa and F Nakamura and Y Maeno},
doi = {10.1088/1742-6596/400/2/022036},
year = {2012},
date = {2012-01-01},
journal = {Journal of Physics: Conference Series},
volume = {400},
number = {PART 2},
abstract = {We study the uniaxial pressure effect on the Mott insulator Ca 2RuO4. It is known that the crystal structure is a crucial parameter to determine the electronic states in this system. We revealed that a metal-insulator(M-I) transition is induced by the uniaxial pressure along the ab-plane at room temperature and the metallic state is sustained under cooling down to 5 K In contrast, such a transition to a metallic state is not observed by the uniaxial pressure along the c-axis. Our experimental results suggest that the elongation of the RuO6 octahedra along the c-axis can trigger the M-I transition. © Published under licence by IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
We study the uniaxial pressure effect on the Mott insulator Ca 2RuO4. It is known that the crystal structure is a crucial parameter to determine the electronic states in this system. We revealed that a metal-insulator(M-I) transition is induced by the uniaxial pressure along the ab-plane at room temperature and the metallic state is sustained under cooling down to 5 K In contrast, such a transition to a metallic state is not observed by the uniaxial pressure along the c-axis. Our experimental results suggest that the elongation of the RuO6 octahedra along the c-axis can trigger the M-I transition. © Published under licence by IOP Publishing Ltd.
718.
D C Peets, G Eguchi, M Kriener, S Harada, Sk.Md. Shamsuzzaman, Y Inada, G -Q Zheng, Y Maeno
Li2(Pd1-xPtx)3B magnetic phase diagram and superconducting parameters Conference
vol. 400, no. PART 2, 2012.
@conference{Peets2012,
title = {Li2(Pd1-xPtx)3B magnetic phase diagram and superconducting parameters},
author = {D C Peets and G Eguchi and M Kriener and S Harada and Sk.Md. Shamsuzzaman and Y Inada and G -Q Zheng and Y Maeno},
doi = {10.1088/1742-6596/400/2/022096},
year = {2012},
date = {2012-01-01},
journal = {Journal of Physics: Conference Series},
volume = {400},
number = {PART 2},
abstract = {Using an ac susceptometry technique, H-T phase diagrams were determined for various Pt contents in the noncentrosymmetric superconducting system Li 2(Pd1-xPtx)3B, from which several superconducting parameters could be extracted. Despite the end compositions having very different band and gap structure and despite a change from singlet- to triplet-dominant pairing, these superconducting parameters change continuously with cation substitution. Weak-coupling BCS and Ginzburg-Landau relations appear to be obeyed, suggesting that this may be a particularly uncomplicated system for studying the effect of a lack of inversion symmetry. © Published under licence by IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
Using an ac susceptometry technique, H-T phase diagrams were determined for various Pt contents in the noncentrosymmetric superconducting system Li 2(Pd1-xPtx)3B, from which several superconducting parameters could be extracted. Despite the end compositions having very different band and gap structure and despite a change from singlet- to triplet-dominant pairing, these superconducting parameters change continuously with cation substitution. Weak-coupling BCS and Ginzburg-Landau relations appear to be obeyed, suggesting that this may be a particularly uncomplicated system for studying the effect of a lack of inversion symmetry. © Published under licence by IOP Publishing Ltd.
717.
R Ishiguro, M Yakabe, T Nakamura, E Watanabe, D Tsuya, H Oosato, Y Maeno, H Takayanagi
Fabrication of SQUIDs with Nb/Ru/Sr2RuO4 junctions Conference
vol. 400, no. PART 2, 2012.
@conference{Ishiguro2012,
title = {Fabrication of SQUIDs with Nb/Ru/Sr2RuO4 junctions},
author = {R Ishiguro and M Yakabe and T Nakamura and E Watanabe and D Tsuya and H Oosato and Y Maeno and H Takayanagi},
doi = {10.1088/1742-6596/400/2/022035},
year = {2012},
date = {2012-01-01},
journal = {Journal of Physics: Conference Series},
volume = {400},
number = {PART 2},
abstract = {We have fabricated superconducting quantum interference devices (SQUIDs) using Nb/Ru/Sr2RuO4 junctions. The superconducting loop of a Nb-Sr2RuO4 hybrid dc SQUID is composed of Nb, Sr 2RuO4 and two Nb/Ru/Sr2RuO4 junctions, and made by building a Nb bridge between two individual Ru micro inclusions on the ab-plane surface of the Ru-Sr2RuO4 eutectic system. We measure the critical current between Nb and Sr 2RuO4 parts of such dc-SQUIDs, which oscillates with every flux quantum through the SQUID loop. © Published under licence by IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
We have fabricated superconducting quantum interference devices (SQUIDs) using Nb/Ru/Sr2RuO4 junctions. The superconducting loop of a Nb-Sr2RuO4 hybrid dc SQUID is composed of Nb, Sr 2RuO4 and two Nb/Ru/Sr2RuO4 junctions, and made by building a Nb bridge between two individual Ru micro inclusions on the ab-plane surface of the Ru-Sr2RuO4 eutectic system. We measure the critical current between Nb and Sr 2RuO4 parts of such dc-SQUIDs, which oscillates with every flux quantum through the SQUID loop. © Published under licence by IOP Publishing Ltd.
716.
J P Carlo, T Goko, I M Gat-Malureanu, P L Russo, A T Savici, A A Aczel, G J MacDougall, J A Rodriguez, T J Williams, G M Luke, C R Wiebe, Y Yoshida, S Nakatsuji, Y Maeno, T Taniguchi, Y J Uemura
New magnetic phase diagram of (Sr,Ca)2 RuO4 Journal Article
In: Nature Materials, vol. 11, no. 4, pp. 323-328, 2012.
@article{Carlo2012323,
title = {New magnetic phase diagram of (Sr,Ca)2 RuO4},
author = {J P Carlo and T Goko and I M Gat-Malureanu and P L Russo and A T Savici and A A Aczel and G J MacDougall and J A Rodriguez and T J Williams and G M Luke and C R Wiebe and Y Yoshida and S Nakatsuji and Y Maeno and T Taniguchi and Y J Uemura},
doi = {10.1038/nmat3236},
year = {2012},
date = {2012-01-01},
journal = {Nature Materials},
volume = {11},
number = {4},
pages = {323-328},
abstract = {High-Tc cuprates, iron pnictides, organic BEDT and TMTSF, alkali-doped C60, and heavy-fermion systems have superconducting states adjacent to competing states exhibiting static antiferromagnetic or spin density wave order. This feature has promoted pictures for their superconducting pairing mediated by spin fluctuations. Sr2RuO4 is another unconventional superconductor which almost certainly has a p-wave pairing. The absence of known signatures of static magnetism in the Sr-rich side of the (Ca, Sr) substitution space, however, has led to a prevailing view that the superconducting state in Sr2RuO4 emerges from a surrounding Fermi-liquid metallic state. Using muon spin relaxation and magnetic susceptibility measurements, we demonstrate here that (Sr,Ca) 2RuO4 has a ground state with static magnetic order over nearly the entire range of (Ca, Sr) substitution, with spin-glass behaviour in Sr1.5Ca0.5RuO4 and Ca1.5Sr 0.5RuO4. The resulting new magnetic phase diagram establishes the proximity of superconductivity in Sr2RuO4 to competing static magnetic order. © 2012 Macmillan Publishers Limited. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
High-Tc cuprates, iron pnictides, organic BEDT and TMTSF, alkali-doped C60, and heavy-fermion systems have superconducting states adjacent to competing states exhibiting static antiferromagnetic or spin density wave order. This feature has promoted pictures for their superconducting pairing mediated by spin fluctuations. Sr2RuO4 is another unconventional superconductor which almost certainly has a p-wave pairing. The absence of known signatures of static magnetism in the Sr-rich side of the (Ca, Sr) substitution space, however, has led to a prevailing view that the superconducting state in Sr2RuO4 emerges from a surrounding Fermi-liquid metallic state. Using muon spin relaxation and magnetic susceptibility measurements, we demonstrate here that (Sr,Ca) 2RuO4 has a ground state with static magnetic order over nearly the entire range of (Ca, Sr) substitution, with spin-glass behaviour in Sr1.5Ca0.5RuO4 and Ca1.5Sr 0.5RuO4. The resulting new magnetic phase diagram establishes the proximity of superconductivity in Sr2RuO4 to competing static magnetic order. © 2012 Macmillan Publishers Limited. All rights reserved.
715.
K Deguchi, S Matsukawa, N K Sato, T Hattori, K Ishida, H Takakura, T Ishimasa
Quantum critical state in a magnetic quasicrystal Journal Article
In: Nature Materials, vol. 11, no. 12, pp. 1013-1016, 2012.
@article{Deguchi20121013,
title = {Quantum critical state in a magnetic quasicrystal},
author = {K Deguchi and S Matsukawa and N K Sato and T Hattori and K Ishida and H Takakura and T Ishimasa},
doi = {10.1038/nmat3432},
year = {2012},
date = {2012-01-01},
journal = {Nature Materials},
volume = {11},
number = {12},
pages = {1013-1016},
abstract = {Quasicrystals are metallic alloys that possess long-range, aperiodic structures with diffraction symmetries forbidden to conventional crystals. Since the discovery of quasicrystals by Schechtman et al. in 1984, there has been considerable progress in resolving their geometric structure. For example, it is well known that the golden ratio of mathematics and art occurs over and over again in their crystal structure. However, the characteristic properties of the electronic states - whether they are extended as in periodic crystals or localized as in amorphous materials - are still unresolved. Here we report the first observation of quantum (T=0) critical phenomena of the Au-Al-Yb quasicrystal - the magnetic susceptibility and the electronic specific heat coefficient arising from strongly correlated 4f electrons of the Yb atoms diverge as T→0. Furthermore, we observe that this quantum critical phenomenon is robust against hydrostatic pressure. By contrast, there is no such divergence in a crystalline approximant, a phase whose composition is close to that of the quasicrystal and whose unit cell has atomic decorations (that is, icosahedral clusters of atoms) that look like the quasicrystal. These results clearly indicate that the quantum criticality is associated with the unique electronic state of the quasicrystal, that is, a spatially confined critical state. Finally we discuss the possibility that there is a general law underlying the conventional crystals and the quasicrystals. © 2012 Macmillan Publishers Limited. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Quasicrystals are metallic alloys that possess long-range, aperiodic structures with diffraction symmetries forbidden to conventional crystals. Since the discovery of quasicrystals by Schechtman et al. in 1984, there has been considerable progress in resolving their geometric structure. For example, it is well known that the golden ratio of mathematics and art occurs over and over again in their crystal structure. However, the characteristic properties of the electronic states - whether they are extended as in periodic crystals or localized as in amorphous materials - are still unresolved. Here we report the first observation of quantum (T=0) critical phenomena of the Au-Al-Yb quasicrystal - the magnetic susceptibility and the electronic specific heat coefficient arising from strongly correlated 4f electrons of the Yb atoms diverge as T→0. Furthermore, we observe that this quantum critical phenomenon is robust against hydrostatic pressure. By contrast, there is no such divergence in a crystalline approximant, a phase whose composition is close to that of the quasicrystal and whose unit cell has atomic decorations (that is, icosahedral clusters of atoms) that look like the quasicrystal. These results clearly indicate that the quantum criticality is associated with the unique electronic state of the quasicrystal, that is, a spatially confined critical state. Finally we discuss the possibility that there is a general law underlying the conventional crystals and the quasicrystals. © 2012 Macmillan Publishers Limited. All rights reserved.
714.
S Kitagawa, K Ishida, T Nakamura, M Matoba, Y Kamihara
Ferromagnetic quantum critical point in heavy-fermion iron oxypnictide Ce(Ru1-xFex)PO Journal Article
In: Physical Review Letters, vol. 109, no. 22, 2012.
@article{Kitagawa2012,
title = {Ferromagnetic quantum critical point in heavy-fermion iron oxypnictide Ce(Ru1-xFex)PO},
author = {S Kitagawa and K Ishida and T Nakamura and M Matoba and Y Kamihara},
doi = {10.1103/PhysRevLett.109.227004},
year = {2012},
date = {2012-01-01},
journal = {Physical Review Letters},
volume = {109},
number = {22},
abstract = {We have performed P31-NMR measurements on Ce(Ru1-xFe x)PO in order to investigate ferromagnetic (FM) quantum criticality, since a heavy-fermion (HF) ferromagnet CeRuPO with a two-dimensional structure turns into a HF paramagnet by an isovalent Fe substitution for Ru. We found that Ce(Ru0.15Fe0.85)PO shows critical fluctuations down to ∼0.3K, as well as the continuous suppression of Curie temperature and the ordered moments by the Fe substitution. These experimental results suggest the presence of a FM quantum critical point (QCP) at x∼0.86, which is a rare example among itinerant ferromagnets. In addition, we point out that the critical behaviors in Ce(Ru0.15Fe0.85)PO share a similarity with those in YbRh2Si2, where the local criticality of f electrons has been discussed. We reveal that Ce(Ru 1-xFex)PO is a new system to study FM quantum criticality in HF compounds. © 2012 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We have performed P31-NMR measurements on Ce(Ru1-xFe x)PO in order to investigate ferromagnetic (FM) quantum criticality, since a heavy-fermion (HF) ferromagnet CeRuPO with a two-dimensional structure turns into a HF paramagnet by an isovalent Fe substitution for Ru. We found that Ce(Ru0.15Fe0.85)PO shows critical fluctuations down to ∼0.3K, as well as the continuous suppression of Curie temperature and the ordered moments by the Fe substitution. These experimental results suggest the presence of a FM quantum critical point (QCP) at x∼0.86, which is a rare example among itinerant ferromagnets. In addition, we point out that the critical behaviors in Ce(Ru0.15Fe0.85)PO share a similarity with those in YbRh2Si2, where the local criticality of f electrons has been discussed. We reveal that Ce(Ru 1-xFex)PO is a new system to study FM quantum criticality in HF compounds. © 2012 American Physical Society.
713.
K Ishida, Y Nakai
Review of NMR studies on iron-based superconductors Book
2012.
@book{Ishida2012275,
title = {Review of NMR studies on iron-based superconductors},
author = {K Ishida and Y Nakai},
doi = {10.4032/9789814303231},
year = {2012},
date = {2012-01-01},
journal = {Iron-based Superconductors: Materials, Properties and Mechanisms},
pages = {275-355},
abstract = {This review presents summary of NMR experiments performed on various iron-based superconductors. The authors introduce NMR experiments which reveal magnetic properties in the normal and superconducting states. In the superconducting state, NMR measurements clarified that iron-based superconductors form spinsinglet pairing, although the orbital symmetry is controversial in some cases. From the comparison of the NMR results in various ironbased superconductors, the relationship between superconductivity and magnetic fluctuations probed with NMR is discussed. © 2013 Pan Stanford Publishing Pte. Ltd. All rights reserved.},
keywords = {},
pubstate = {published},
tppubtype = {book}
}
This review presents summary of NMR experiments performed on various iron-based superconductors. The authors introduce NMR experiments which reveal magnetic properties in the normal and superconducting states. In the superconducting state, NMR measurements clarified that iron-based superconductors form spinsinglet pairing, although the orbital symmetry is controversial in some cases. From the comparison of the NMR results in various ironbased superconductors, the relationship between superconductivity and magnetic fluctuations probed with NMR is discussed. © 2013 Pan Stanford Publishing Pte. Ltd. All rights reserved.
712.
K Karube, T Hattori, S Kitagawa, K Ishida, N Kimura, T Komatsubara
Universality and critical behavior at the critical endpoint in the itinerant-electron metamagnet UCoAl Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 86, no. 2, 2012.
@article{Karube2012,
title = {Universality and critical behavior at the critical endpoint in the itinerant-electron metamagnet UCoAl},
author = {K Karube and T Hattori and S Kitagawa and K Ishida and N Kimura and T Komatsubara},
doi = {10.1103/PhysRevB.86.024428},
year = {2012},
date = {2012-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {86},
number = {2},
abstract = {We performed nuclear-magnetic-resonance measurements on itinerant-electron metamagnet UCoAl to investigate the critical behavior of the magnetism near a metamagnetic (MM) critical endpoint (CEP). We derived c-axis magnetization M c and its fluctuation S c from the measurements of Knight shift and nuclear spin-lattice relaxation rate 1/T 1 as a function of the c-axis external field (H c) and temperature (T). We developed contour plots of M c and S c on the H c-T phase diagram, and observed the strong divergence of S c at the CEP. The critical exponents of M c and S c near the CEP are estimated and found to be close to the universal properties of a three-dimensional Ising model. We indicate that the critical phenomena at the itinerant-electron MM CEP in UCoAl have a common feature as a gas-liquid transition. © 2012 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We performed nuclear-magnetic-resonance measurements on itinerant-electron metamagnet UCoAl to investigate the critical behavior of the magnetism near a metamagnetic (MM) critical endpoint (CEP). We derived c-axis magnetization M c and its fluctuation S c from the measurements of Knight shift and nuclear spin-lattice relaxation rate 1/T 1 as a function of the c-axis external field (H c) and temperature (T). We developed contour plots of M c and S c on the H c-T phase diagram, and observed the strong divergence of S c at the CEP. The critical exponents of M c and S c near the CEP are estimated and found to be close to the universal properties of a three-dimensional Ising model. We indicate that the critical phenomena at the itinerant-electron MM CEP in UCoAl have a common feature as a gas-liquid transition. © 2012 American Physical Society.
711.
T Iye, Y Nakai, S Kitagawa, K Ishida, S Kasahara, T Shibauchi, Y Matsuda, T Terashima
Gradual suppression of antiferromagnetism in BaFe 2(As 1-xP x) 2: Zero-temperature evidence for a quantum critical point Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 85, no. 18, 2012.
@article{Iye2012,
title = {Gradual suppression of antiferromagnetism in BaFe 2(As 1-xP x) 2: Zero-temperature evidence for a quantum critical point},
author = {T Iye and Y Nakai and S Kitagawa and K Ishida and S Kasahara and T Shibauchi and Y Matsuda and T Terashima},
doi = {10.1103/PhysRevB.85.184505},
year = {2012},
date = {2012-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {85},
number = {18},
abstract = {Static and dynamic magnetic properties of lightly P-substituted BaFe 2(As 1-xP x) 2 were systematically investigated by 31P NMR. The averaged internal magnetic field at the P site in the zero-temperature limit evaluated from the broadening of NMR spectra in the antiferromagnetic (AFM) phase is gradually suppressed toward x∼0.35 with increasing x, which provides definitive evidence for the existence of an AFM quantum critical point (QCP) at x∼0.35. The location of the AFM QCP is consistent with the previous estimation from temperature dependence of spin dynamics in the normal state, and the superconducting transition temperature T c takes the maximum around the QCP. Our experiments, revealing a signature of a QCP extending up to room temperature, establish BaFe 2(As 1-xP x) 2 as one of the most accessible systems for unraveling the nature of quantum criticality and the relationship between AFM quantum criticality and unconventional superconductivity. © 2012 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Static and dynamic magnetic properties of lightly P-substituted BaFe 2(As 1-xP x) 2 were systematically investigated by 31P NMR. The averaged internal magnetic field at the P site in the zero-temperature limit evaluated from the broadening of NMR spectra in the antiferromagnetic (AFM) phase is gradually suppressed toward x∼0.35 with increasing x, which provides definitive evidence for the existence of an AFM quantum critical point (QCP) at x∼0.35. The location of the AFM QCP is consistent with the previous estimation from temperature dependence of spin dynamics in the normal state, and the superconducting transition temperature T c takes the maximum around the QCP. Our experiments, revealing a signature of a QCP extending up to room temperature, establish BaFe 2(As 1-xP x) 2 as one of the most accessible systems for unraveling the nature of quantum criticality and the relationship between AFM quantum criticality and unconventional superconductivity. © 2012 American Physical Society.
710.
Y Nakai, S Kitagawa, T Iye, K Ishida, Y Kamihara, M Hirano, H Hosono
Enhanced anisotropic spin fluctuations below tetragonal-to-orthorhombic transition in LaFeAs(O 1-xF x) probed by 75As and 139La NMR Journal Article
In: Physical Review B - Condensed Matter and Materials Physics, vol. 85, no. 13, 2012.
@article{Nakai2012,
title = {Enhanced anisotropic spin fluctuations below tetragonal-to-orthorhombic transition in LaFeAs(O 1-xF x) probed by 75As and 139La NMR},
author = {Y Nakai and S Kitagawa and T Iye and K Ishida and Y Kamihara and M Hirano and H Hosono},
doi = {10.1103/PhysRevB.85.134408},
year = {2012},
date = {2012-01-01},
journal = {Physical Review B - Condensed Matter and Materials Physics},
volume = {85},
number = {13},
abstract = {75As and 139La NMR results for LaFeAs(O 1-xF x) (x=0, 0.025, and 0.04) are reported. Upon F doping, the tetragonal-to-orthorhombic structural phase transition temperature T S, antiferromagnetic transition temperature T N, and internal magnetic field μ 0H int are gradually reduced for x<0.04. However, at x=0.04, T N is abruptly suppressed to be 30 K along with a tiny μ 0H int, which is distinct from the continuous disappearance of the ordered phases in the Ba122 systems of Ba(Fe,Co) 2As 2 and BaFe 2(As,P) 2. The anisotropy of the spin-lattice relaxation rate T1-1, (T 1)H∥ab-1/ (T 1)H∥c-1, in the paramagnetic phase of x=0 and 0.025 is constant (∼1.5) but increases abruptly below T S due to the enhancement of (T 1)H∥ab-1 by the slowing-down of magnetic fluctuations. This indicates that the tetragonal-to-orthorhombic structural distortion enhances the anisotropy in the spin space via magnetoelastic coupling and/or spin-orbit interaction. © 2012 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
75As and 139La NMR results for LaFeAs(O 1-xF x) (x=0, 0.025, and 0.04) are reported. Upon F doping, the tetragonal-to-orthorhombic structural phase transition temperature T S, antiferromagnetic transition temperature T N, and internal magnetic field μ 0H int are gradually reduced for x<0.04. However, at x=0.04, T N is abruptly suppressed to be 30 K along with a tiny μ 0H int, which is distinct from the continuous disappearance of the ordered phases in the Ba122 systems of Ba(Fe,Co) 2As 2 and BaFe 2(As,P) 2. The anisotropy of the spin-lattice relaxation rate T1-1, (T 1)H∥ab-1/ (T 1)H∥c-1, in the paramagnetic phase of x=0 and 0.025 is constant (∼1.5) but increases abruptly below T S due to the enhancement of (T 1)H∥ab-1 by the slowing-down of magnetic fluctuations. This indicates that the tetragonal-to-orthorhombic structural distortion enhances the anisotropy in the spin space via magnetoelastic coupling and/or spin-orbit interaction. © 2012 American Physical Society.
709.
T Iye, Y Nakai, S Kitagawa, K Ishida, S Kasahara, T Shibauchi, Y Matsuda, T Terashima
Microscopic evidence of direct coupling between magnetic and superconducting order parameters in BaFe 2(As 1-xP x) 2 Journal Article
In: Journal of the Physical Society of Japan, vol. 81, no. 3, 2012.
@article{Iye2012b,
title = {Microscopic evidence of direct coupling between magnetic and superconducting order parameters in BaFe 2(As 1-xP x) 2},
author = {T Iye and Y Nakai and S Kitagawa and K Ishida and S Kasahara and T Shibauchi and Y Matsuda and T Terashima},
doi = {10.1143/JPSJ.81.033701},
year = {2012},
date = {2012-01-01},
journal = {Journal of the Physical Society of Japan},
volume = {81},
number = {3},
abstract = {The coexistence of magnetism and superconductivity in the isovalent-P-substituted BaFe 2(As 1-xP x) 2 has been investigated microscopically by 31P-NMR measurements. We found that superconducting (SC) transition occurs in a magnetic region with static ordered moments and that the moments are reduced below the SC transition temperature T c in the samples near the phase boundary of magnetism and superconductivity. Our results indicate that magnetism and superconductivity coexist spatially but compete with each other on the same Fermi surfaces. The coexistence state is qualitatively different from that observed in other unconventional superconductors and gives a strict constraint on the theoretical model for superconductivity in BaFe 2(As 1-xP x) 2. © 2012 The Physical Society of Japan.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The coexistence of magnetism and superconductivity in the isovalent-P-substituted BaFe 2(As 1-xP x) 2 has been investigated microscopically by 31P-NMR measurements. We found that superconducting (SC) transition occurs in a magnetic region with static ordered moments and that the moments are reduced below the SC transition temperature T c in the samples near the phase boundary of magnetism and superconductivity. Our results indicate that magnetism and superconductivity coexist spatially but compete with each other on the same Fermi surfaces. The coexistence state is qualitatively different from that observed in other unconventional superconductors and gives a strict constraint on the theoretical model for superconductivity in BaFe 2(As 1-xP x) 2. © 2012 The Physical Society of Japan.
708.
T Hattori, Y Ihara, Y Nakai, K Ishida, Y Tada, S Fujimoto, N Kawakami, E Osaki, K Deguchi, N K Sato, I Satoh
Superconductivity induced by longitudinal ferromagnetic fluctuations in UCoGe Journal Article
In: Physical Review Letters, vol. 108, no. 6, 2012.
@article{Hattori2012,
title = {Superconductivity induced by longitudinal ferromagnetic fluctuations in UCoGe},
author = {T Hattori and Y Ihara and Y Nakai and K Ishida and Y Tada and S Fujimoto and N Kawakami and E Osaki and K Deguchi and N K Sato and I Satoh},
doi = {10.1103/PhysRevLett.108.066403},
year = {2012},
date = {2012-01-01},
journal = {Physical Review Letters},
volume = {108},
number = {6},
abstract = {From detailed angle-resolved NMR and Meissner measurements on a ferromagnetic (FM) superconductor UCoGe (T Curie∼2.5K and T SC∼0.6K), we show that superconductivity in UCoGe is tightly coupled with longitudinal FM spin fluctuations along the c axis. We found that magnetic fields along the c axis (Hc) strongly suppress the FM fluctuations and that the superconductivity is observed in the limited magnetic-field region where the longitudinal FM spin fluctuations are active. These results, combined with model calculations, strongly suggest that the longitudinal FM spin fluctuations tuned by Hc induce the unique spin-triplet superconductivity in UCoGe. This is the first clear example that FM fluctuations are intimately related with superconductivity. © 2012 American Physical Society.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
From detailed angle-resolved NMR and Meissner measurements on a ferromagnetic (FM) superconductor UCoGe (T Curie∼2.5K and T SC∼0.6K), we show that superconductivity in UCoGe is tightly coupled with longitudinal FM spin fluctuations along the c axis. We found that magnetic fields along the c axis (Hc) strongly suppress the FM fluctuations and that the superconductivity is observed in the limited magnetic-field region where the longitudinal FM spin fluctuations are active. These results, combined with model calculations, strongly suggest that the longitudinal FM spin fluctuations tuned by Hc induce the unique spin-triplet superconductivity in UCoGe. This is the first clear example that FM fluctuations are intimately related with superconductivity. © 2012 American Physical Society.
707.
K Ishida, M Ogata
Preface Journal Article
In: Journal of the Physical Society of Japan, vol. 81, no. 1, 2012.
@article{Ishida2012b,
title = {Preface},
author = {K Ishida and M Ogata},
year = {2012},
date = {2012-01-01},
journal = {Journal of the Physical Society of Japan},
volume = {81},
number = {1},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
706.
S Kitagawa, Y Nakai, T Iye, K Ishida, Y F Guo, Y G Shi, K Yamaura, E Takayama-Muromachi
vol. 391, no. 1, 2012.
@conference{Kitagawa2012b,
title = {Nuclear spin-lattice relaxation rate in the superconducting state on La(Fe1-xZnx)AsO0.85 studied by 75As-NMR},
author = {S Kitagawa and Y Nakai and T Iye and K Ishida and Y F Guo and Y G Shi and K Yamaura and E Takayama-Muromachi},
doi = {10.1088/1742-6596/391/1/012130},
year = {2012},
date = {2012-01-01},
journal = {Journal of Physics: Conference Series},
volume = {391},
number = {1},
abstract = {75As nuclear spin-lattice relaxation rate 1/T1 was measured in Zn-free and Zn-substituted La(Fe1-xZnx)AsO0.85 (x 0, and 0.05), Tc of which is 25 K and 0 K, respectively. Although the temperature dependence of 1/T1T above Tc is the same between two samples, 1/T1T of x 0 shows T 3.0±0.1 dependence (1/T1 T4) in the superconducting (SC) state, but 1/T1T of non-SC x 0.05 sample continuously decreases below 50 K. The normalized 1/T1T [(1/T1T)x=0/(1/T1T)x=0.05], which is related to the SC gap structure, is proportional to T2.4±0.1 below Tc. These results indicate that the temperature dependence of 1/T1T in the SC state can be affected by the temperature dependence of the normal-state 1/T1T. © Published under licence by IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
75As nuclear spin-lattice relaxation rate 1/T1 was measured in Zn-free and Zn-substituted La(Fe1-xZnx)AsO0.85 (x 0, and 0.05), Tc of which is 25 K and 0 K, respectively. Although the temperature dependence of 1/T1T above Tc is the same between two samples, 1/T1T of x 0 shows T 3.0±0.1 dependence (1/T1 T4) in the superconducting (SC) state, but 1/T1T of non-SC x 0.05 sample continuously decreases below 50 K. The normalized 1/T1T [(1/T1T)x=0/(1/T1T)x=0.05], which is related to the SC gap structure, is proportional to T2.4±0.1 below Tc. These results indicate that the temperature dependence of 1/T1T in the SC state can be affected by the temperature dependence of the normal-state 1/T1T. © Published under licence by IOP Publishing Ltd.
705.
T Hattori, Y Ihara, K Karube, Y Nakai, K Ishida, K Deguchi, N K Sato, I Satoh
Anisotropic magnetic fluctuations and superconductivity in ferromagnetic superconductor UCoGe Conference
vol. 391, no. 1, 2012.
@conference{Hattori2012b,
title = {Anisotropic magnetic fluctuations and superconductivity in ferromagnetic superconductor UCoGe},
author = {T Hattori and Y Ihara and K Karube and Y Nakai and K Ishida and K Deguchi and N K Sato and I Satoh},
doi = {10.1088/1742-6596/391/1/012017},
year = {2012},
date = {2012-01-01},
journal = {Journal of Physics: Conference Series},
volume = {391},
number = {1},
abstract = {We have performed 59Co NQR / NMR measurements on the single-crystalline UCoGe, in order to investigate the relationship between ferromagnetism and superconductivity. The measurements of Knight-shift and nuclear spin-lattice relaxation rate provide clear evidence that both static and dynamic susceptibilities are ferromagnetic with Ising anisotropy. In addition, Hc2 also shows extremely large anisotropy which can not be explained by the GL model with anisotropy of effective mass. These data suggest intimate relationship between Ising magnetization and anisotropic superconductivity in UCoGe. © Published under licence by IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
We have performed 59Co NQR / NMR measurements on the single-crystalline UCoGe, in order to investigate the relationship between ferromagnetism and superconductivity. The measurements of Knight-shift and nuclear spin-lattice relaxation rate provide clear evidence that both static and dynamic susceptibilities are ferromagnetic with Ising anisotropy. In addition, Hc2 also shows extremely large anisotropy which can not be explained by the GL model with anisotropy of effective mass. These data suggest intimate relationship between Ising magnetization and anisotropic superconductivity in UCoGe. © Published under licence by IOP Publishing Ltd.
704.
T Iye, Y Nakai, S Kitagawa, K Ishida, H Ikeda, S Kasahara, T Shibauchi, Y Matsuda, T Terashima
P-concentration dependence of the quasiparticle density of states in BaFe2(As1-xPx)2 Conference
vol. 391, no. 1, 2012.
@conference{Iye2012c,
title = {P-concentration dependence of the quasiparticle density of states in BaFe2(As1-xPx)2},
author = {T Iye and Y Nakai and S Kitagawa and K Ishida and H Ikeda and S Kasahara and T Shibauchi and Y Matsuda and T Terashima},
doi = {10.1088/1742-6596/391/1/012127},
year = {2012},
date = {2012-01-01},
journal = {Journal of Physics: Conference Series},
volume = {391},
number = {1},
abstract = {31P-NMR measurements were performed in the iron pnictides BaFe2(As1-xPx)2 for 0.07 ≤ x ≤ 0.64 in order to investigate evolution of electronic state with isovalent substitution. In general, the spin part of the Knight shift Kspin and (T1T)-1/2 are proportional to the quasiparticle density of states at the Fermi level N(EF) at high temperature where the Korringa relation holds. We found that Kspin and (T1T)-1/2 are almost unaffected by the P-substitution, indicating that N(EF) is nearly constant. These results are quantitatively consistent with our band calculation. We claim that the slight changes of N(EF) by P-substitution in BaFe2(As1-xPx)2 is not enough to explain the Tc variation ranging from 30 K to 0 K, and thus suggest that antiferromagnetic correlations related to the quantum critical character are essential for the high Tc superconductivity. © Published under licence by IOP Publishing Ltd.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
31P-NMR measurements were performed in the iron pnictides BaFe2(As1-xPx)2 for 0.07 ≤ x ≤ 0.64 in order to investigate evolution of electronic state with isovalent substitution. In general, the spin part of the Knight shift Kspin and (T1T)-1/2 are proportional to the quasiparticle density of states at the Fermi level N(EF) at high temperature where the Korringa relation holds. We found that Kspin and (T1T)-1/2 are almost unaffected by the P-substitution, indicating that N(EF) is nearly constant. These results are quantitatively consistent with our band calculation. We claim that the slight changes of N(EF) by P-substitution in BaFe2(As1-xPx)2 is not enough to explain the Tc variation ranging from 30 K to 0 K, and thus suggest that antiferromagnetic correlations related to the quantum critical character are essential for the high Tc superconductivity. © Published under licence by IOP Publishing Ltd.
