Publication list

@article{NishiZaki19991581,

title = {Effect of Impurities on the Specific Heat of the Spin-Triplet Superconductor Sr2RuO4},

author = {S NishiZaki and Y Maeno and Z Mao},

year  = {1999},

date = {1999-01-01},

journal = {Journal of Low Temperature Physics},

volume = {117},

number = {5-6},

pages = {1581-1585},

abstract = {We have investigated the specific heat of single crystals of the spin-triplet superconductor Sr2RuO4 (Tc0 = 1.50 K) with various Tc. We focus on the Tc dependence of the specific heat jump at Tc and of the residual specific heat coefficient. The observed behavior is not quantitatively consistent with a model with a simple isotropic gap. We argue that inclusions of both the in-plane anisotropy of the gap and the dependence of the gap on different Fermi-surface sheets are needed to resolve this discrepancy.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Maeno1999535,

title = {Experimental evidence for spin-triplet superconductivity in Sr2RuO4},

author = {Y Maeno and S NishiZaki and Z Q Mao},

year  = {1999},

date = {1999-01-01},

journal = {Journal of Superconductivity and Novel Magnetism},

volume = {12},

number = {4},

pages = {535-541},

abstract = {We review the experimental evidence for spin-triplet superconductivity in Sr2RuO4. The Knight shift experiments decisively demonstrated that the Cooper-pair symmetry is spin triplet. We discuss the most probable wave function of the Cooper pairs on the basis of the results of a number of key experiments. We point out that a simple picture of the unitary state with the isotropic gap is not compatible with the observed behavior of the specific heat, and that a profound modification of the pairing wave function is needed. We also present the in-plane angular dependence of the upper critical field, with the field applied exactly parallel to the quasi-two-dimensional plane. We discuss the possible implication of the observed fourfold anisotropy in connection with the proposed second superconducting state with a line-node gap. © 1999 Plenum Publishing Corporation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mukuda19991587,

title = {17 O Knight shift study in the superconducting state of Sr2RuO4},

author = {H Mukuda and K Ishida and Y Kitaoka and Z Mao and Y Mori and Y Maeno},

year  = {1999},

date = {1999-01-01},

journal = {Journal of Low Temperature Physics},

volume = {117},

number = {5-6},

pages = {1587-1591},

abstract = {17 O Knight shift measurements in Sr2RuO4 were performed over the wide range of magnetic field 3.2-11.4kOe parallel to the basal RuO2 planes. The spin susceptibility is totally unchanged through its Tc, evidencing that the spin-triplet superconducting state is realized in Sr2RuO4. The result indicates that the Cooper pairs consist of the parallel spin pairs | ↑↑> and | ↑↑> with their quantization axis perpendicular to the c-axis direction. The in-plane 2D nearly ferromagnetic spin fluctuations may play a role for the stabilization of this state among various representations of spin-triplet order parameter.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Sidis19993320,

title = {Evidence for incommensurate spin fluctuations in Sr2RuO4},

author = {Y Sidis and M Braden and P Bourges and B Hennion and S Nishi Zaki and Y Maeno and Y Mori},

doi = {10.1103/PhysRevLett.83.3320},

year  = {1999},

date = {1999-01-01},

journal = {Physical Review Letters},

volume = {83},

number = {16},

pages = {3320-3323},

abstract = {We report inelastic neutron scattering measurements in the normal state of Sr2RuO4 that reveal the existence of significant incommensurate magnetic spin fluctuations located at q0= (± 0.6 π/a, ± 0.6 π/a,0) . This finding confirms recent band-structure calculations that have predicted incommensurate magnetic responses related to dynamical nesting properties of its Fermi surface and points towards the possibility of a competition between p -wave spin triplet and d -wave spin singlet superconductivity in Sr2RuO4 . We present a comparison between low energy spin fluctuations, converted in absolute units, from inelastic neutron scattering measurements and previous nuclear magnetic resonance studies. 1999 © The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Maeno199970,

title = {Metal - Insulator transitions in layered ruthenates},

author = {Y Maeno and S Nakatsuji and S Ikeda},

doi = {10.1016/S0921-5107(99)00054-9},

year  = {1999},

date = {1999-01-01},

journal = {Materials Science and Engineering B: Solid-State Materials for Advanced Technology},

volume = {63},

number = {1-2},

pages = {70-75},

abstract = {We present the phenomenological systematics of a series of ruthenates, (Ca, Sr)n+1 RunO3n+1, which exhibits a rich variety of ground states. We will also discuss in some detail the physical properties of the two-dimensional Mott-transition system, Ca2-xSrxRuO4 in which the Mott insulator Ca2RuO4 evolves into the spin-triplet superconductor Sr2RuO4 by means of a band-width control. © 1999 Elsevier Science S.A. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kitaoka199983,

title = {NMR probe of magnetism and superconductivity in ruthenate oxides},

author = {Y Kitaoka and K Ishida and H Mukuda and Z Q Mao and S Ikeda and S Nishizaki and Y Maeno and R Kanno and M Takano},

doi = {10.1016/S0921-5107(99)00056-2},

year  = {1999},

date = {1999-01-01},

journal = {Materials Science and Engineering B: Solid-State Materials for Advanced Technology},

volume = {63},

number = {1},

pages = {83-87},

abstract = {We review recent NMR investigations on superconducting and magnetic properties in layered perovskite Sr2RuO4, isostructural to a high-Tc cuprate. Measurements of the Knight shift and the nuclear spin-lattice relaxation rate 1/T1 have identified its Cooper-pair spin state as a triplet and uncovered pronounced anisotropy in spin-fluctuation spectrum in Sr2RuO4. The in-plane low-frequency components of the dynamical susceptibility are exchange-enhanced with a weak q dependence associated with the two-dimensional (2D) character in electronic structure. By contrast, its out-of-plane component is unexpectedly enhanced by AF spin fluctuations upon cooling below T* to approximately 130 K where the c-axis resistivity shows metallic behavior. We have found that the slightly-distorted cubic perovskite CaRuO3 is a nearly ferromagnetic metal dominated by ferromagnetic spin fluctuations with a Stoner factor α = 0.98. Contrasting behavior of spin fluctuations between Sr2RuO4 and CaRuO3 is due to their different dimensionality in electronic structure with the closeness to ferromagnetism. We remark that a simple ferromagnetic-spin-fluctuation-mediated mechanism with analogy to 3He is not appropriate for an onset of spin-triplet p-wave superconductivity in Sr2RuO4. Alternately, we propose possible scenario that the in-plane local exchange interaction, which originates presumably from the Hund's coupling between the 4dxy and 4dxz, yz orbitals, may play a role for the occurrence of spin-triplet p-wave superconductivity.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ohmichi19991912,

title = {Resistance peak under a magnetic field parallel to the conducting plane},

author = {E Ohmichi and H Adachi and Y Maeno and T Ishiguro and T Komatsu and G Saito},

doi = {10.1016/S0379-6779(98)00619-5},

year  = {1999},

date = {1999-01-01},

journal = {Synthetic Metals},

volume = {103},

number = {1-3},

pages = {1912},

abstract = {In this study, an attempt was made to measure the sharp magnetoresistance peak for the two-dimensional conductors, κ-(BEDT-TTF)2Cu2(CN)3 and Sr2RuO4. It was found that the peak height depends on the orientation of the magnetic field within the conducting plane. The band calculation revealed that the calculated warping pattern is most prominent for the direction corresponding to the observed peak.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ikeda1999947,

title = {Magnetic properties of bilayered Sr3Ru2O7},

author = {S -I Ikeda and Y Maeno},

doi = {10.1016/S0921-4526(98)01012-6},

year  = {1999},

date = {1999-01-01},

journal = {Physica B: Condensed Matter},

volume = {259-261},

pages = {947-948},

abstract = {We have grown single crystalline Sr3Ru2O7 by a floating-zone method. The lattice parameters and field dependence of magnetization are remarkably different between the floating-zone and the flux-method crystals. While the flux-method crystal is a ferromagnet with Tc = 104 K, the floating-zone crystal is a paramagnet. This difference reflects that metallic Sr3Ru2O7 is intrinsically in the vicinity of a strong ferromagnetic instability. © 1999 Elsevier Science B.V. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ohmichi199924,

title = {Enhancement of the sum and difference frequencies in Shubnikov-de Haas oscillation at Yamaji angle in the layered perovskite Sr2RuO4},

author = {E Ohmichi and Y Maeno and T Ishiguro},

doi = {10.1143/JPSJ.68.24},

year  = {1999},

date = {1999-01-01},

journal = {Journal of the Physical Society of Japan},

volume = {68},

number = {1},

pages = {24-27},

abstract = {With regard to the Shubnikov-de Haas oscillations in Sr2RuO4, an unusual enhancement was found in oscillatory components with frequencies Fβ±α = Fβ ± Fα for a particular orientation of the crystal in the magnetic field, where Fα and Fβ are the oscillatory frequencies for the two-dimensional Fermi surface branches, α and β, respectively. The orientation is given by the so-called Yamaji angles corresponding to the maxima in the angle-dependent magnetoresistance oscillation, where the carriers in the slightly warped cylindrical Fermi surface behave as if they were in a two-dimensional system. The results can be understood in terms of the chemical potential oscillation effect as predicted by Nakano for de Haas-van Alphen oscillations.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Akima1999694,

title = {Intrinsic superconducting parameters of Sr2RuO4},

author = {T Akima and S Nishizaki and Y Maeno},

doi = {10.1143/JPSJ.68.694},

year  = {1999},

date = {1999-01-01},

journal = {Journal of the Physical Society of Japan},

volume = {68},

number = {2},

pages = {694-695},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mao1999610,

title = {Suppression of superconductivity in Sr2RuO4 caused by defects},

author = {Z Q Mao and Y Mori and Y Maeno},

doi = {10.1103/PhysRevB.60.610},

year  = {1999},

date = {1999-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {60},

number = {1},

pages = {610-614},

abstract = {We have investigated depairing effects in Sr2RuO4, the unconventional superconductor in the layered perovskite structure. We prepared crystals of Sr2RuO4 with very low levels of impurity elements, and systematically controled their superconducting transition temperature Tc ranging from 1.5 to 0.6 K by adjustments of crystal growth conditions. The dependence of Tc on the residual resistivity ρ0 in these crystals suggests that the defects are strong pair breakers, in addition to impurities. We further characterized the effects of pair breaking in this unconventional superconductor. We found that the in-plane coherence length ξab(0) evaluated from Hc2(T) is inversely proportional to Tc, and decreases with increasing mean free path l; the latter behavior is opposite to that of conventional superconductors. In addition, we examined the temperature dependence of Hc2∥c which substantially deviates from the BCS theory and even from a recent theory of a p-wave superconductor. © 1999 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nakatsuji1999949,

title = {Metal insulator transition in Ca2-xSrxRuO4},

author = {S Nakatsuji and T Ando and Z Mao and Y Maeno},

doi = {10.1016/S0921-4526(98)00995-8},

year  = {1999},

date = {1999-01-01},

journal = {Physica B: Condensed Matter},

volume = {259-261},

pages = {949-950},

abstract = {We have newly synthesized Ca2-xSrxRuO4 in the whole region of x: the two-dimensional Mott-transition system which continuously connects the Mott insulating Ca2RuO4 with the superconducting Sr2RuO4. The metal-insulator transition occurs in Ca rich region by varying either Sr content or temperature. © 1999 Elsevier Science B.V. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mota1999934,

title = {Transition into a low temperature superconducting phase of unconventional pinning in Sr2RuO4},

author = {A C Mota and E Dumont and A Amann and Y Maeno},

doi = {10.1016/S0921-4526(98)00963-6},

year  = {1999},

date = {1999-01-01},

journal = {Physica B: Condensed Matter},

volume = {259-261},

pages = {934-935},

abstract = {We have found a sharp transition in the vortex creep rates at a temperature T* = 0.05Tc in a single crystal of Sr2RuO4 (Tc = 1.03 K) by means of magnetic relaxation measurements. For T < T*, the initial creep rates drop to undetectably low levels. One explanation for this transition into a phase with such extremely low vortex creep is that the low-temperature phase of Sr2RuO4 breaks time reversal symmetry. In that case, degenerate domain walls separating discreetly degenerate states of a superconductor can act as very strong pinning centers [M. Sigrist, K. Ueda, Rev. Mod. Phys. 63 (1992) 239]. © 1999 Elsevier Science B.V. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ando19991651,

title = {Upper critical fields of the 3-K superconducting phase of Sr2RuO4},

author = {T Ando and T Akima and Y Mori and Y Maeno},

doi = {10.1143/JPSJ.68.1651},

year  = {1999},

date = {1999-01-01},

journal = {Journal of the Physical Society of Japan},

volume = {68},

number = {5},

pages = {1651-1656},

abstract = {We have investigated the normal-state and superconducting properties of the 3-K superconducting phase of Sr2RuO4 with the enhanced transition temperature Tc by lamellae of ruthenium metal. In contrast to the dimensional crossover in the metallic conduction in pure Sr2RuCO4 with Tc = 1.5 K, the 3-K phase retains metallic interlayer conduction at least up to 300 K. We attribute this behavior to the interlayer metallic paths through the Ru lamellae, connected by in-plane current paths. For the superconducting properties, the phase diagram of the anisotropic upper critical fields Hc2(T) indicates that Hc2//ab is strongly suppressed in the low-temperature region. The measurements of the out-of-plane resistivity ρc under magnetic fields show that the finite residual resistivity recovers above Hc2(T) of pure Sr2RuO4. This result confirms the spatial coexistence of the enhanced superconductivity with the Tc = 1.5-K region in the 3-K superconductor. In addition, we have also observed hysteresis in ρc, which appear only in the 3-K phase at low temperatures and in high fields parallel to the RuO2 plane.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ohmichi19997263,

title = {Angle-dependent magnetoresistance oscillation in the layered perovskite Sr2RuO4},

author = {E Ohmichi and H Adachi and Y Mori and Y Maeno and T Ishiguro and T Oguchi},

doi = {10.1103/PhysRevB.59.7263},

year  = {1999},

date = {1999-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {59},

number = {11},

pages = {7263-7265},

abstract = {The Fermi surface topology of the layered perovskite Sr2RuO4 was investigated through the observation of angle-dependent magnetoresistance oscillation under a magnetic field up to 17 T at 1.5 K. A series of angles giving the resistance peaks, observed under a constant field above 5 T, can be assigned to the Fermi wave-number vector of both the α and β branches of the calculated Fermi surface. © 1999 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Jin19994433,

title = {Observation of anomalous temperature dependence of the critical current in (formula presented) junctions},

author = {R Jin and Y Zadorozhny and Y Liu and D G Schlom and Y Mori and Y Maeno},

doi = {10.1103/PhysRevB.59.4433},

year  = {1999},

date = {1999-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {59},

number = {6},

pages = {4433-4438},

abstract = {We have studied the temperature dependence of the critical current (Formula presented) of bilayer (Formula presented) junctions prepared by using a submicron-diameter filament as a shadow mask. (Formula presented) a layered perovskite isostructural with (Formula presented) has a superconducting transition temperature (Formula presented) lower than that of Pb. Below the (Formula presented) of Pb, the critical current (Formula presented) of the junction was found to increase initially with decreasing temperature. As the temperature was lowered to below the (Formula presented) of (Formula presented) however, a sharp drop in (Formula presented) was observed. This downturn in (Formula presented) suggests that superconductivity in (Formula presented) actually suppresses the Josephson coupling between the two Pb electrodes, which are conventional s-wave superconductors. The implications of this unexpected behavior will be explored, in particularly, in the context of the pairing symmetry in (Formula presented). © 1999 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mukuda1999944,

title = {17O NMR probe of spin fluctuations in triplet superconductor Sr2RuO4},

author = {H Mukuda and K Ishida and Y Kitaoka and K Asayama and Z -Q Mao and Y Mori and Y Maeno},

doi = {10.1016/S0921-4526(98)01037-0},

year  = {1999},

date = {1999-01-01},

journal = {Physica B: Condensed Matter},

volume = {259-261},

pages = {944-946},

abstract = {From the 17O Knight shift measurements on O(1) in RuO2 planes and O(2) in SrO layers in Sr2RuO4 with Tc = 1.5 K, it is shown that the distribution of the spin density at the O(1) sites reflects two-dimensional electronic structure with most of its fraction on the in-plane pπ orbitals. From systematic measurements of the nuclear spin-lattice relaxation rate, T1-1, it is found that dynamical susceptibility is highly anisotropic in contrast to the uniform susceptibility being isotropic. Their in-plane components for the O(1) sites are almost independent of wavenumber although they are exchange-enhanced, whereas it is unexpected that the out-of-plane component being q dependent is pronouncedly enhanced by interlayer antiferromagnetic spin fluctuations below T* ∼ 130 K where the c-axis resistivity shows a metallic behavior. These novel characters of spin fluctuations are suggested to lead to discussions about a possible mechanism of spin-triplet p-wave superconductivity in Sr2RuO4. © 1999 Elsevier Science B.V. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Bergemann1999444,

title = {Quantum oscillations and overcritical torque interaction in Sr2RuO4},

author = {C Bergemann and S R Julian and A P Mackenzie and A W Tyler and D E Farrell and Y Maeno and S Nishizaki},

doi = {10.1016/S0921-4534(99)00095-7},

year  = {1999},

date = {1999-01-01},

journal = {Physica C: Superconductivity and its Applications},

volume = {317-318},

pages = {444-447},

abstract = {Sr2RuO4 is the only known layered perovskite oxide superconductor without copper; there is strong evidence for an unconventional ('p-wave') pairing mechanism, and it has recently been shown to possess a cylindrical, 'quasi-two-dimensional' Fermi surface. Using Sr2RuO4 as a test case for the detection of quantum oscillations with piezoresistive microcantilevers, the piezolever torque magnetometry technique was successfully implemented on a dilution refrigerator. It was possible to reproduce the quantum-oscillatory magnetization data on all three Fermi surface sheets, in a crystal of microgram mass. Moreover, an absolute estimate of the amplitude of the oscillation is provided. We also investigated the phenomenon of torque interaction which distorts the magnetization signal and introduces harmonics and sidebands to the dHvA spectrum. As the torque interaction effect grows in strength, overcritically is shown to lead to discrete magnetization jumps and to a near-asymptotically damped 'sproing' effect.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Julian1999928,

title = {Normal state, superconductivity and quasiparticle Fermi surface of the strongly correlated oxide Sr2RuO4},

author = {S R Julian and A P Mackenzie and G G Lonzarich and C Bergemann and R K W Haselwimmer and Y Maeno and S NishiZaki and A W Tyler and S Ikeda and T Fujita},

doi = {10.1016/S0921-4526(98)00820-5},

year  = {1999},

date = {1999-01-01},

journal = {Physica B: Condensed Matter},

volume = {259-261},

pages = {928-933},

abstract = {The oxide superconductor Sr2RuO4 is emerging as an archetypal strongly correlated electron system. We review the experimental situation, focusing on Fermi surface specific probes. Quantum oscillation measurements have revealed a Fermi surface consisting of three slightly warped cylinders populated by quasiparticles with masses ranging from 3.4 to 14.6 times the bare electron mass. There is strong evidence that Sr2RuO4 is a spin-triplet superconductor, and the simplicity of the Fermi surface combined with detailed knowlege of the quasiparticle properties from quantum oscillation and orbital specific NMR measurements means that Sr2RuO4 may be a key system for understanding unconventional superconductivity. We compare Sr2RuO4 with three-dimensional nearly ferromagnetic 3d-metals, and suggest that quasi-two-dimensional spin-fluctuations may be responsible for the fact that Sr2RuO4 is the first nearly ferromagnetic metal to show superconductivity. © 1999 Elsevier Science B.V. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Asayama19983207,

title = {NMR of high-T c superconductors},

author = {K Asayama and Y Kitaoka and G -Q Zheng and K Ishida and K Magishi and Y Tokunaga and K Yoshida},

year  = {1998},

date = {1998-01-01},

journal = {International Journal of Modern Physics B},

volume = {12},

number = {29-31},

pages = {3207-3215},

abstract = {Recent NMR measurements on high-T c materials by our group are reviewed. Study of YBa 2Cu 3O 7+Ni has revealed that the attractive force is spin in origin. Analysis of T 1, the Knight shift K and T 2G in Tl 2Ba 2Ca 2CuO 10 (T12223), HgBa 2Ca 2Cu 3O 8 (Hg1223), HgBa 2Ca 3Cu 4O 10 (Hg1234) and YBa 2Cu 4O 8 (Y1248) supports the antiferromagnetic spin fluctuation (AFSF)-rnediated-superconductivity-model. The temperatures at which a pseudogap starts to open obtained by 1/T 1T, dK/dT, photoemission, resistivity and STM all agree with each other in Bi 2Sr 2CaCu 2O 8 (Bi2212). The origin of the pseudogap is discussed.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mukuda19982101,

title = {Ru NQR probe of superconducting property in impurity-doped CeRu2},

author = {H Mukuda and K Ishida and Y Kitaoka and K Asayama},

doi = {10.1143/JPSJ.67.2101},

year  = {1998},

date = {1998-01-01},

journal = {Journal of the Physical Society of Japan},

volume = {67},

number = {6},

pages = {2101-2106},

abstract = {Superconducting characteristics of CeRu2 have been investigated by systematic measurements of the nuclear-spin lattice relaxation rate, 1/T1 of 101Ru on pure and impurity-substituted CeRu2, employing an NQR technique in zero magnetic field. (1/T1) for CeRu2 shows a broad coherence plateau just below Tc followed by an exponential decrease well below Tc. By contrast, a distinct coherence peak of (1/T1) has been found just below Tc for the impurity-substituted CeRu2, even though La- and Al-substitutions for the Ce and Ru sites make Tc slightly increase and decrease, respectively. It is considered that the impurity scattering averages out the anisotropy of the energy gap, in good agreement with the theory of dirty superconductors by Anderson. 101(1/T1T) in the normal state, which is in proportion to the square of the density of states at the Fermi level, N2(EF), is found to decrease with the Al content. The suppression in Tc by substituting nonmagnetic Al impurity for the Ru sites is well accounted for by an appreciable reduction in N(EF). The present Ru NQR study has revealed that CeRu2 is characterized as a conventional s-wave superconductor with a large anisotropic energy gap.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mukuda19982163,

title = {Ru NQR study in A1-doped CeRu2},

author = {H Mukuda and K Ishida and Y Kitaoka and K Asayama},

doi = {10.1016/S0022-3697(98)00203-0},

year  = {1998},

date = {1998-01-01},

journal = {Journal of Physics and Chemistry of Solids},

volume = {59},

number = {10-12},

pages = {2163-2165},

abstract = {Superconducting characteristics of Ce(Ru1-xAlx)2 (x = 0, 0.01, 0.03), which shows quite unconventional behavior on the impurity effect has been investigated by the nuclear-spin lattice relaxation rate, 1/T1 of 101Ru, employing an NQR technique in zero magnetic field. The suppression in Tc by substituting non-magnetic Al impurity for Ru site is well accounted for by an appreciable reduction in N(EF). Pure and Al-doped CeRu2 can be explained within the framework of the BCS theory by incorporating the variation of DOS at the Fermi level. © 1998 Elsevier Science Ltd. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kawasaki19988634,

title = {Si-NMR study of antiferromagnetic heavy-fermion compounds and},

author = {Y Kawasaki and K Ishida and Y Kitaoka and K Asayama},

doi = {10.1103/PhysRevB.58.8634},

year  = {1998},

date = {1998-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {58},

number = {13},

pages = {8634-8639},

abstract = {We report Si-NMR studies on the magnetic property of pressure-induced superconductors (Formula presented) and (Formula presented) which exhibit antiferromagnetic (AF) order with the Néel temperature (Formula presented) K and 36 K at ambient pressure, respectively. The NMR results in (Formula presented) are consistent with those obtained from the previous neutron-diffraction (ND) experiments. On the other hand, the NMR study in oriented powder (Formula presented) has revealed that the spectrum splits into two peaks due to the onset of the AF order with the wave vector of (Formula presented) below (Formula presented) and each peak splits further into two peaks below (Formula presented) due to the formation of AF domains with (Formula presented) The saturation moment (Formula presented) and (Formula presented) estimated from NMR are significantly smaller than (Formula presented) and (Formula presented) from ND. From this discrepancy in the sizes of (Formula presented) it is proposed that a correlation time in fluctuations of f-electron moments is longer than the characteristic time of observation for thermal neutrons but shorter than that for NMR. This probe dependence of (Formula presented) was observed in the uranium heavy-fermion (HF) compounds (Formula presented) and (Formula presented) From the temperature dependence of the nuclear spin-lattice relaxation rate (Formula presented) in the paramagnetic state, the Kondo temperature (Formula presented) in (Formula presented) is estimated to be around (Formula presented) much higher than (Formula presented) in (Formula presented) The (Formula presented)’s in both the compounds decrease markedly below (Formula presented) followed by a (Formula presented) constant behavior far below (Formula presented) From the latter result, it is suggested that low-lying excitations at low temperatures are dominated by quasiparticle excitations in the AF ordered state in (Formula presented) and (Formula presented). © 1998 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Thessieu1998487,

title = {NMR Study of MnSi under Pressure},

author = {C Thessieu and K Ishida and Y Kitaoka and K Asayama and G Lapertot},

doi = {10.4131/jshpreview.7.487},

year  = {1998},

date = {1998-01-01},

journal = {Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu},

volume = {7},

pages = {487-489},

abstract = {The magnetic phase diagram TC(P) of the weak itinerant helimagnetic compound MnSi is reviewed upon a Nuclear Magnetic Resonance (NMR) experiment. We present a systematic study on the evolution of the NMR spin echo signal at T=1.4 K of the non-magnetic silicone sites, 29Si, up to 17.8 kbar. The pressure effect is interpreted as a weak variation of the local electronic spin polarization and the coexistence of magnetic and non magnetic Mn atoms under pressure. From the volume dependence of f0(P), we show notably that a local magnetic order remains above the critical pressure of Pc=14.8 kbar. [Weakly Itinerant Helimagnetism, Nuclear Magnetic Resonance, Hydrostatic Pressure]. © 1998, The Japan Society of High Pressure Science and Technology. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida19981289,

title = {Low-temperature thermal properties of the werner calibrate inclusion compounds. Isotopic p-xylenes in tetrakis (4-methylpyridine) nickel(ii) thiocyanate a},

author = {K Ishida and T Matsuo and H Suga and W Zielenkiewicz and J Lipkowski},

doi = {10.1006/jcht.1998.0392},

year  = {1998},

date = {1998-01-01},

journal = {Journal of Chemical Thermodynamics},

volume = {30},

number = {11},

pages = {1289-1306},

abstract = {The heat capacities of the clathrate compounds formed by inclusion of p-C6H4(CH3)2 and p-C6D4(CD3)2 in tetrakis(4-methylpyridine) nickel(II) thiocyanate, and the empty host compound have been measured at temperatures between (12 and 300) K. Two temperature regions of anomalous heat capacity were found for each of the clathrate compounds. The molar heat capacity divided by the temperature (Cp,m/T) plotted against the temperature gave clear representation of the anomalies, making it possible to estimate the temperature, enthalpy, and entropy associated with the heat capacity peaks. Standard thermodynamic functions were calculated and tabulated for rounded temperatures. These data were combined with those of p-xylene to give the entropy of clathrate formation. Experimental evidence is presented that helium is captured into the empty host cavity to form a clathrate compound at low temperatures. © 1998 Academic Press.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Thessieu1998609,

title = {Pressure effect on MnSi: An NMR study},

author = {C Thessieu and K Ishida and Y Kitaoka and K Asayama and G Lapertot},

doi = {10.1016/S0304-8853(97)00478-2},

year  = {1998},

date = {1998-01-01},

journal = {Journal of Magnetism and Magnetic Materials},

volume = {177-181},

number = {PART 1},

pages = {609-610},

abstract = {The itinerant weakly helimagnetic compound MnSi has been investigated from zero-field NMR measurements on the nonmagnetic 29Si sites in the ordered state under hydrostatic pressure up to 17.8 kbar. The characteristic evolution of the resonance spectrum and the nuclear relaxation time T1 is addressed with increasing pressure. Our results show clearly the existence of a remaining local magnetic order above the critical pressure Pc = 14.8 kbar. From 1/T1T = const. relation at low temperature, we extract information concerning the evolution of the density of states at the Fermi level N(εF) as function of pressure. © 1998 Elsevier Science B.V. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Magishi199811533,

title = {Spin gap and dynamics in comprising hole-doped two-leg spin ladders: Cu NMR study on single crystals},

author = {K Magishi and S Matsumoto and Y Kitaoka and K Ishida and K Asayama},

doi = {10.1103/PhysRevB.57.11533},

year  = {1998},

date = {1998-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {57},

number = {18},

pages = {11533-11544},

abstract = {We report comprehensive Cu NMR studies on single crystals of (Formula presented) which contain simple (Formula presented) chains and two-leg (Formula presented) ladders. From measurements of the (Formula presented) NMR shift, it is clear that the spin gap in the ladders decreases with isovalent Ca substitution from (Formula presented) K for (Formula presented) (Sr14) to (Formula presented) K, (Formula presented) K, and (Formula presented) K for (Formula presented) (Ca6), (Formula presented) (Ca9), and (Formula presented) (Ca11.5), respectively. The exponential decrease of the nuclear spin-lattice relaxation rate (Formula presented) below ∼130 K is consistent with the presence of the spin gap in the spin excitation spectrum. In the (Formula presented) range higher than (Formula presented) K, we observed the following dependences: (Formula presented) and the square of Gaussian spin-echo decay time, (Formula presented) which are consistent with the scaling theory for the (Formula presented) one-dimensional (1D) Heisenberg model. The value of (Formula presented) is compatible with the theoretical prediction of an exchange constant along the leg (Formula presented) K for Ca6 and (Formula presented) K for Ca9 and Ca11.5. A notable finding is that the magnitude of the spin gap remains nearly constant and characteristics of novel 1D-like spin dynamics are maintained in the content varying from Ca9 to Ca11.5. On the other hand, the charge transport changes with increasing Ca content so that the more conductive Ca11.5 exhibits pressure-induced superconductivity exceeding 3.5 GPa. We have found that (Formula presented), which is proportional to the inverse spin correlation length (Formula presented), deviates from a linear (Formula presented) dependence upon cooling and is described by (Formula presented), regardless of the Ca substitution. We point out that the value of (Formula presented) is proportional to the finite value of (Formula presented) where (Formula presented) is the spin-wave velocity. From the result that the values of (Formula presented) for Ca6, Ca9, and Ca11.5 are significantly reduced compared to that for Sr14, it is suggested that (Formula presented) is dominated at low (Formula presented) by an average distance (Formula presented) among mobile holes obeying the relation (Formula presented) From an estimate of (Formula presented) 5.2 for Sr14, where (Formula presented) is the Cu-Cu distance along the leg, (Formula presented) is obtained as (Formula presented), 2.3, and 2.0, and hole content (Formula presented) as (Formula presented), 0.22, and 0.25 per (Formula presented) ladder for Ca6, Ca9, and Ca11.5, respectively. These values were consistent with (Formula presented) 0.14, 0.2, and 0.22 for Ca6, Ca9, and Ca11 estimated from the optical conductivity experiment by Osafune et al. [Phys. Rev. Lett. 78, 1980 (1997)]. The (Formula presented) compounds are thus hole-doped two-leg spin-ladder systems which reveal the metallic behavior dominated by the 1D-like spin dynamics at high (Formula presented) and accompanied by the spin gap formation at low (Formula presented). For Ca11.5, as the spin gap is formed upon cooling below (Formula presented) K, the resistivity increases in the direction perpendicular to the ladder, whereas the conductivity along the ladder remains metallic, followed by the localization of mobile holes in both directions below (Formula presented) K. We point out that preformed pairs are confined in each ladder and localized below (Formula presented) K at an ambient pressure. © 1998 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida1998R11054,

title = {Ru NMR and NQR probes of the metamagnetic transition},

author = {K Ishida and Y Kawasaki and Y Kitaoka and K Asayama and H Nakamura},

doi = {10.1103/PhysRevB.57.R11054},

year  = {1998},

date = {1998-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {57},

number = {18},

pages = {R11054-R11057},

abstract = {We report (Formula presented) NMR and NQR studies on (Formula presented) in a magnetic field (Formula presented) range of 0-15.5 T across the metamagnetic transition at (Formula presented) T. From measurements of the hyperfine field, (Formula presented) at the Ru sites induced by the (Formula presented)-spin polarization and the nuclear-spin lattice relaxation rate, (Formula presented), three heavy-fermion (HF) regimes have been clarified. (1) For (Formula presented) T, the HF state is formed below 8 K. (2) At (Formula presented) T, (Formula presented) continues to increase upon cooling to 1.4 K, suggesting a very low characteristic energy. (3) In the polarized state above (Formula presented) the (Formula presented) probing the quasiparticle excitation is dramatically suppressed at low (Formula presented), accompanying a peak at high (Formula presented). The crossover in the HF state takes place not only in the (Formula presented) variation but also in the (Formula presented) variation across the metamagnetic transition in (Formula presented). © 1998 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tou19983129,

title = {Nonunitary spin-triplet superconductivity in UPt3: Evidence from 195Pt knight shift study},

author = {H Tou and Y Kitaoka and K Ishida and K Asayama and N Kimura and Y O Nuki and E Yamamoto and Y Haga and K Maezawa},

doi = {10.1103/PhysRevLett.80.3129},

year  = {1998},

date = {1998-01-01},

journal = {Physical Review Letters},

volume = {80},

number = {14},

pages = {3129-3132},

abstract = {195Pt Knight shift (KS) measurements covering the superconducting multiple phases for major field (H) orientations have been carried out on the high-quality single crystal UPt3. For H > 5 kOe, the KS does not change below the superconducting transition temperature Tc down to 28 mK, regardless of major crystal orientations, which provides evidence that the odd-parity superconductivity with the parallel spin pairing is realized. By contrast, the KS decreases below Tc for Hb||b axis and Hb < 5 kOe and for Hc||c axis and Hc <.3 kOe, whereas the KS for HA||A axis is T independent across Tc down to Ha˜1.764 kOe. These novel findings entitle UPt3 as the first spin-triplet odd-parity superconductor including a nonunitary pairing characterized by the two-component d vector like db+idc at low T and low H. © 1998 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kitaoka1998487,

title = {Systematic NMR studies of high-Tc and two-leg spin-ladder systems},

author = {Y Kitaoka and K Magishi and S Matsumoto and K Ishida and S Ohsugi and K Asayama and M Uehara and T Nagata and J Akimitsu},

doi = {10.1016/S0304-8853(97)00613-6},

year  = {1998},

date = {1998-01-01},

journal = {Journal of Magnetism and Magnetic Materials},

volume = {177-181},

number = {PART 1},

pages = {487-492},

abstract = {We review systematic NMR studies on underdoped high-Tc, cuprates and two-leg spin-ladder systems, focusing on their spin gap and dynamics. The pressure-induced superconductivity was discovered in Sr14-xCaxCu24O41 comprising the quasi-one-dimensional S = 1/2 two-leg spin-ladder Cu2O3 planes. Remarkably, the new parent cuprate is the Mott insulator with the spin gap in contrast to the antiferromagnetic (AF) insulator for the high-Tc cuprates. From the Cu-NMR results in the ladder Cu2O3 plane on single crystals Sr14-xCaxCu24O41 with x = 9 (hereafter denoted as Ca9) and x = 11.5 (Ca11.5), it is shown that the spin gap, Δ = 510 K in the Sr14 is significantly reduced upon isovalent Ca substitution, but its magnitude remains nearly constant with Δ = 270 and 280 K for the Ca9 and Ca11.5, respectively. In T range of T ≥ Δ, the spin dynamics in carrier-doped two-leg spin-ladder systems are characterized by the behaviour similar to the S = 1/2 1D Heisenberg system. By contrast, the transport property shares a common feature, i.e, due to the spin-gap opening the charge transport is confined in the 2D CuO2 plane for underdoped high-Tc cuprates and in the quasi-1D ladder for spin-ladder compounds. © 1998 Elsevier Science B.V. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida1998R5960,

title = {Pseudogap behavior in single-crystal probed by Cu NMR},

author = {K Ishida and K Yoshida and T Mito and Y Tokunaga and Y Kitaoka and K Asayama and Y Nakayama and J Shimoyama and K Kishio},

doi = {10.1103/PhysRevB.58.R5960},

year  = {1998},

date = {1998-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {58},

number = {10},

pages = {R5960-R5963},

abstract = {We report that the nuclear spin-lattice relaxation rate divided by temperature, (Formula presented) has a broad maximum around (Formula presented) and ∼100 K in underdoped and overdoped single crystals of (Formula presented) (Bi2212) with (Formula presented) and 77.3 K, respectively, showing the normal-state spin-gap behavior. One result is that the steep decrease in the (Formula presented)Cu Knight shift, (Formula presented) has been observed below (Formula presented) and ∼100 K, suggesting the normal-state pseudogap behavior in quasiparticle density of states (DOS), which is consistent with the pseudogap behavior below (Formula presented) revealed on underdoped Bi2212 from studies of angle-resolved photoemission spectroscopy. We propose that the spin-gap behavior in (Formula presented) has the same origin as the pseudogap in the quasiparticle DOS. © 1998 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Imada1998387,

title = {Photoemission of CeX2Y2 and Ce(Pd1-xCux)3},

author = {S Imada and M Tsunekawa and T Iwasaki and S Suga and Y Onuki and F Iga and M Kasaya and Y Kawasaki and K Ishida and Y Kitaoka and K Asayama},

doi = {10.1016/S0304-8853(97)00510-6},

year  = {1998},

date = {1998-01-01},

journal = {Journal of Magnetism and Magnetic Materials},

volume = {177-181},

number = {PART 1},

pages = {387-388},

abstract = {A high-resolution valence-band photoemission study on various Ce compounds is presented. The intensity of the features just below the Fermi energy is quite sensitive to the Kondo temperature. On the other hand, the overall shape of the whole 4f spectrum is strongly affected by the overall hybridization between the 4f state and the valence band. © 1998 Elsevier Science B.V. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida1998658,

title = {Spin-triplet superconductivity in Sr2RuO4 identified by 17O knight shift},

author = {K Ishida and H Mukuda and Y Kitaoka and K Asayama and Z Q Mao and Y Mori and Y Maeno},

doi = {10.1038/25315},

year  = {1998},

date = {1998-01-01},

journal = {Nature},

volume = {396},

number = {6712},

pages = {658-660},

abstract = {Superconductivity - one of the best understood many-body problems in physics - has again become a challenge following the discovery of unconventional superconducting materials: these include heavy-fermion, organic and the high-transition-temperature copper oxide superconductors. In conventional superconductors, the electrons form superconducting Cooper pairs in a spin-singlet state, which has zero total spin (S = 0). In principle, Cooper pairs can also form in a spin-triplet state (S = 1), analogous to the spin-triplet 'p-wave' state of paired neutral fermions in superfluid 3He (ref. 4). At present, the heavy-fermion compound UPt3 is the only known spin-triplet superconductor, although the layered oxide superconductor Sr2RuO4 (ref. 7) is believed, on theoretical grounds, to be a promising candidate. The most direct means of identifying the spin state of Cooper pairs is from measurements of their spin susceptibility, which can be determined by the Knight shift (as probed by nuclear magnetic resonance (NMR). Here we report Knight-shift measurements of Sr2RuO2 using 17O NMR. Our results show no change in spin susceptibility on passing through the superconducting transition temperature, which provides the definitive identification of Sr2RuO4 as a spin-triplet superconductor. Superconductivity - one of the best understood many-body problems in physics - has again become a challenge following the discovery of unconventional superconducting materials: these include heavy-fermion, organic and the high-transition-temperature copper oxide superconductors. In conventional superconductors, the electrons form superconducting Cooper pairs in a spin-singlet state, which has zero total spin (S = 0). In principle, Cooper pairs can also form in a spin-triplet state (S = 1), analogous to the spin-triplet 'p-wave' state of paired neutral fermions in superfluid 3He (ref. 4). At present, the heavy-fermion compound UPt3 is the only known spin-triplet superconductor, although the layered oxide superconductor Sr2RuO4 (ref. 7) is believed, on theoretical grounds, to be a promising candidate. The most direct means of identifying the spin state of Cooper pairs is from measurements of their spin susceptibility, which can be determined by the Knight shift (as probed by nuclear magnetic resonance (NMR)). Here we report Knight-shift measurements of Sr2RuO2 using 17O NMR. Our results show no change in spin susceptibility on passing through the superconducting transition temperature, which provides the definitive identification of Sr2RuO4 as a spin-triplet superconductor.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Riseman1998242,

title = {Observation of a square flux-line lattice in the unconventional superconductor Sr2RuO4},

author = {T M Riseman and P G Kealey and E M Forgan and A P Mackenzie and L M Galvin and A W Tyler and S L Lee and C Ager and D.McK. Paul and C M Aegerter and R Cubitt and Z Q Mao and T Akima and Y Maeno},

doi = {10.1038/24335},

year  = {1998},

date = {1998-01-01},

journal = {Nature},

volume = {396},

number = {6708},

pages = {242-245},

abstract = {The phenomenon of superconductivity continues to be of considerable scientific and practical interest. Underlying this phenomenon is the formation of electron pairs, which in conventional superconductors do not rotate about their centre of mass ('s-wave' pairing; refs 1, 2). This contrasts with the situation in high-temperature superconductors, where the electrons in a pair are believed to have two units of relative angular momentum ('d-wave' pairing; ref. 3 and references therein). Here we report small-angle neutron-scattering measurements of magnetic flux lines in the perovskite superconductor Sr2RuO4 (ref. 4), which is a candidate for another unconventional paired electron state - 'p-wave' pairing, which has one unit of angular momentum. We find that the magnetic flux lines form a square lattice over a wide range of fields and temperatures, which is the result predicted by a recent theory of p-wave superconductivity in Sr2RuO4. This theory also indicates that only a fraction of the electrons are strongly paired and that the orientation of the square flux lattice relative to the crystal lattice will determine which parts of the three-sheet Fermi surface of this material are responsible for superconductivity. Our results suggest that superconductivity resides mainly on the 'γ' sheet.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Maeno19983765,

title = {Enhancement of superconductivity of Sr2RuO4 to 3 K by embedded metallic microdomains},

author = {Y Maeno and T Ando and Y Mori and E Ohmichi and S Ikeda and S Nishizaki and S Nakatsuji},

doi = {10.1103/PhysRevLett.81.3765},

year  = {1998},

date = {1998-01-01},

journal = {Physical Review Letters},

volume = {81},

number = {17},

pages = {3765-3768},

abstract = {We have found that the quasi-two-dimensional superconductor Sr2RuO4 with the intrinsic transition temperature Tc = 1.5 K exhibits a remarkable enhancement in Tc up to 3 K, if lamellar microdomains of ruthenium metal are embedded. Measurements of the anisotropy in the upper critical fields indicate that the 3-K superconductivity is sustained essentially in the layered structure of Sr2RuO4. We suggest that the enhanced interlayer coherence provided via metallic Ru plays a key role in the doubling of Tc. © 1998 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Suderow1998,

title = {Very low temperature thermal conductivity in the layered perovskite superconductor Sr2RuO4},

author = {H Suderow and J P Brison and J Flouquet and A W Tyler and Y Maeno},

doi = {10.1088/0953-8984/10/34/004},

year  = {1998},

date = {1998-01-01},

journal = {Journal of Physics Condensed Matter},

volume = {10},

number = {34},

pages = {L597-L602},

abstract = {We present thermal conductivity measurements on the layered perovskite superconductor Sr2RuO4 down to very low temperatures (20 mK). Our data show a large residual term in κ/T as T → 0 K which depends on the sample quality. We do not observe any sign of the predicted crossover at low temperatures or of a second phase transition at least above 20 mK.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Luke1998558,

title = {Time-reversal symmetry-breaking superconductivity in SR2RuO4},

author = {G M Luke and Y Fudamoto and K M Kojima and M I Larkin and J Merrin and B Nachumi and Y J Uemura and Y Maeno and Z Q Mao and Y Mori and H Nakamura and M Sigrist},

doi = {10.1038/29038},

year  = {1998},

date = {1998-01-01},

journal = {Nature},

volume = {394},

number = {6693},

pages = {558-561},

abstract = {Although the properties of most superconducting materials are well described by the theory of Bardeen, Cooper and Schrieffer (BCS), considerable effort has been devoted to the search for exotic superconducting systems in which BCS theory does not apply. The transition to the superconducting state in conventional BCS superconductors involves the breaking of gauge symmetry only, whereby the wavefunction describing the Cooper pairs - the paired electron states responsible for superconductivity - adopt a definite phase. In contrast, a signature of an unconventional superconducting state is the breaking of additional symmetries, which can lead to anisotropic pairing (such as the 'd-wave' symmetry observed in the copper oxide superconductors) and the presence of multiple superconducting phases (as seen in UPt3 and analogous behaviour in superfluid 3He; refs 3-5). Here we report muon spin- relaxation measurements on the superconductor Sr2RuO4 that reveal the spontaneous appearance of an internal magnetic field below the transition temperature: the appearance of such a field indicates that the superconducting state in this material is characterized by the breaking of time-reversal symmetry. These results, combined with other symmetry considerations, suggest that superconductivity in Sr2RuO4 is of 'p-wave' (odd-parity) type, analogous to superfluid 3He.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ikeda1998978,

title = {Weak ferromagnetism in two-dimensional bilayered},

author = {S Ikeda and Y Maeno},

doi = {10.1103/PhysRevB.57.978},

year  = {1998},

date = {1998-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {57},

number = {2},

pages = {978-986},

abstract = {We have synthesized a bilayered ruthenate solid solution Sr(Formula presented)Ca(Formula presented)Ru(Formula presented)O(Formula presented), which is homologous to the copper-free layered-perovskite superconductor Sr(Formula presented)RuO(Formula presented)=1.5 K). The (Formula presented) dependence of the lattice parameters, magnetic susceptibility (Formula presented), magnetization (Formula presented), and electrical resistivity (Formula presented) is systematically examined. Samples for all (Formula presented) show magnetic ordering below 150 K. It is shown, however, that the magnetic correlations change with increasing Ca content. The lowest ferromagnetic-ordering temperature in this series is observed at 3.2 K in the sample with (Formula presented)(Ca) =1.0. This transition is described well as a weakly ferromagnetic ordering by self-consistent renormalization (SCR) theory of spin fluctuations. To the best of our knowledge, this is the first example of applying the SCR theory to a weak ferromagnet with a quasi-two-dimensional layered crystal structure. © 1998 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Shirakawa1998499,

title = {Pressure Effect on Superconductivity and Normal State of Sr2RuO},

author = {N Shirakawa and K Murata and Y Maeno and T Fujita},

doi = {10.4131/jshpreview.7.499},

year  = {1998},

date = {1998-01-01},

journal = {Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu},

volume = {7},

pages = {499-501},

abstract = {We studied electrical resistivity and the Hall coefficient of single-crystalline samples of an oxide superconductor Sr2RuO4 under hydrostatic pressures up to 1.2 GPa. The value of Tc decreases by ~ 36 % at 1.2 GPa, while no appreciable change in the resistivity or the Hall coefficient has been observed. At room temperature an unexpected increase of resistivity along the c axis occurs with increasing pressure. [Sr2RuO4, superconductivity, Tc, resistivity, the Hall coefficient]. © 1998, The Japan Society of High Pressure Science and Technology. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tyler1998R10107,

title = {High-temperature resistivity of Bad metallic transport in a good metal},

author = {A Tyler and A Mackenzie and S NishiZaki and Y Maeno},

doi = {10.1103/PhysRevB.58.R10107},

year  = {1998},

date = {1998-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {58},

number = {16},

pages = {R10107-R10110},

abstract = {We report the results of a study of the in-plane and out-of-plane resistivity of the layered perovskite superconductor (Formula presented) at temperatures between 4 and 1300 K. Although the material is a very good metal at low temperatures, with in-plane mean free paths (l) of thousands of lattice spacings, l falls smoothly to less than 1 Å at 1300 K with no sign of resistivity saturation at the Mott-Ioffe-Regel limit. Measurements of the incoherent out-of-plane resistivity over the same range of temperature are also discussed. © 1998 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nishizaki1998560,

title = {Evidence for Unconventional Superconductivity of Sr2RuO4 from Specific-Heat Measurements},

author = {S Nishizaki and Y Maeno and S Farner and S -I Ikeda and T Fujita},

doi = {10.1143/JPSJ.67.560},

year  = {1998},

date = {1998-01-01},

journal = {Journal of the Physical Society of Japan},

volume = {67},

number = {2},

pages = {560-563},

abstract = {We measured the specific heat of single crystals of non-cuprate layered perovskite superconductor Sr2RuO4. The crystals with different Tc up to 1.2 K exhibit a large residual electronic coefficient γ0, which decreases systematically with increasing Tc. This behavior is consistent with the presence of nodes in the superconducting gap and with the variations of Tc due to pair breaking by impurities and defects. To quantitatively account for the observed large γ0, however, we need to introduce additional mechanism.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Hussey19985505,

title = {Normal-state magnetoresistance},

author = {N Hussey and A Mackenzie and J Cooper and Y Maeno and S Nishizaki},

doi = {10.1103/PhysRevB.57.5505},

year  = {1998},

date = {1998-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {57},

number = {9},

pages = {5505-5511},

abstract = {We report measurements of the in-plane and out-of-plane magnetoresistance (MR) of single crystals of the layered perovskite superconductor (Formula presented) The transverse (Formula presented)-axis MR (Formula presented) varies linearly with field at low temperatures consistent with the behavior expected for a quasi-two-dimensional Fermi surface in the intermediate-field regime. (Formula presented) shows a striking temperature dependence which arises from the competing effects of two separate MR contributions. At low temperatures, (Formula presented) is large and positive due to the orbital magnetoresistance of the carriers. At high temperatures, however, (Formula presented) is dominated by a negative MR term that is associated with the nonmetallic out-of-plane resistivity (Formula presented) We argue that the two contributions to (Formula presented) originate from separate conduction channels along the (Formula presented) axis and that the competition between the metallic and nonmetallic channels is responsible for the unusual temperature dependence of (Formula presented) Finally, we discuss the relevance of these findings to our current understanding of the unusual magnetoresistance of the high-(Formula presented) cuprates. © 1998 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mackenzie1998385,

title = {The Fermi Surface Topography of Sr2RuO4},

author = {A P Mackenzie and S -I Ikeda and Y Maeno and T Fujita and S R Julian and G G Lonzarich},

doi = {10.1143/JPSJ.67.385},

year  = {1998},

date = {1998-01-01},

journal = {Journal of the Physical Society of Japan},

volume = {67},

number = {2},

pages = {385-388},

abstract = {Although angle-resolved photoemission spectroscopy (ARPES) has been used for detailed study of the layered perovskite copper-oxside superconductors for nearly ten years,Sr2RuO4 is the first metal of this structural class for which it has been possible to obtin detailed Fermi Surface data from both quantum oscillations and ARPES. We show that two techniques give very different results, and present strong evidence that the current interpretation of ARPES data is not representative of the bulk electronic structure of Sr2RuO4.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mackenzie1998161,

title = {Extremely Strong Dependence of Superconductivity on Disorder in Sr2RuO4},

author = {A P Mackenzie and R K W Haselwimmer and A W Tyler and G G Lonzarich and Y Mori and S Nishizaki and Y Maeno},

doi = {10.1103/PhysRevLett.80.161},

year  = {1998},

date = {1998-01-01},

journal = {Physical Review Letters},

volume = {80},

number = {1},

pages = {161-164},

abstract = {A key signature of unconventional or non-s-wave superconductivity is a strong suppression of Tc by nonmagnetic as well as by magnetic impurities. We report measurements of chemical composition and of transport properties in the same single crystals of Sr2RuO4 which show that nonmagnetic impurities destroy superconductivity when the residual resistivity exceeds 1 μΩ cm, i.e., when the carrier mean free path falls below the superconducting coherence length. This behavior strongly supports models of non-s-wave (e.g., p-or d-wave) pairing in this layered perovskite oxide. © 1998 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Inoue19982205,

title = {Spectral weight redistribution in a layered 4d-electron superconductor Sr2RuO4},

author = {I H Inoue and A Kimura and A Harasawa and A Kakizaki and Y Aiura and S Ikeda and Y Maeno},

doi = {10.1016/S0022-3697(98)00209-1},

year  = {1998},

date = {1998-01-01},

journal = {Journal of Physics and Chemistry of Solids},

volume = {59},

number = {10-12},

pages = {2205-2207},

abstract = {The ultraviolet photoemission spectrum of a layered-perovskite superconductor Sr2RuO4 around the Fermi level is considerably different from the density of states obtained by a band calculation based on the local density approximation. Although the significant spectral weight redistribution is considered to be evidence of the large electron correlation in this system, the effective mass is not so enhanced. A possible scenario to coordinate both these phenomena is discussed. © 1998 Elsevier Science Ltd. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Yoshida199815062,

title = {Electronic crossover in the highly anisotropic normal state of from pressure effects on electrical resistivity},

author = {K Yoshida and F Nakamura and T Goko and T Fujita and Y Maeno and Y Mori and S NishiZaki},

doi = {10.1103/PhysRevB.58.15062},

year  = {1998},

date = {1998-01-01},

journal = {Physical Review B - Condensed Matter and Materials Physics},

volume = {58},

number = {22},

pages = {15062-15066},

abstract = {We investigated pressure dependence of the electrical resistivity of the only copper-free layered-perovskite superconductor (Formula presented) The characteristic temperature (Formula presented) where the out-of-plane resistivity (Formula presented) changes from metallic behavior to nonmetallic behavior with increasing temperature, increases with hydrostatic pressure. In contrast, the absolute value of (Formula presented) at (Formula presented) is almost independent of pressure. Such a change over in (Formula presented) is ascribable to the crossover from the diffusion process of quasiparticles between the adjacent layers to the thermally assisted hopping process. The pressure effects on (Formula presented) are possibly characterized by the enhanced transfer integral along the c axis by pressure. On the other hand, in the temperature dependence of the in-plane resistivity, we observed an intriguing hump that appears at low T less than (Formula presented) in the pressure range from 1.5 to 5 GPa, and vanishes on applying higher pressure. This behavior may be comprehensible from the view of the two-dimensional ferromagnetic spin fluctuations enhanced by pressure. © 1998 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mukuda19983945,

title = {Novel Character of Spin Fluctuations in Spin-Triplet Superconductor Sr2RuO4: 17O-NMR Study},

author = {H Mukuda and K Ishida and Y Kitaoka and K Asayama and Z Mao and Y Mori and Y Maeno},

doi = {10.1143/JPSJ.67.3945},

year  = {1998},

date = {1998-01-01},

journal = {Journal of the Physical Society of Japan},

volume = {67},

number = {11},

pages = {3945-3951},

abstract = {We report 17O-NMR studies in the normal state of high-quality single-crystal Sr2RuO4 with Tc ∼1.5 K, which has been identified as spin-triplet p-wave superconductor. From systematic measurements of the Knight shift and the nuclear spin-lattice relaxation time T1 on the O(1) sites in the RuO2 planes and the O(2) sites in the SrO layers, microscopic distribution of the spin density on the p Orbitals and the anisotropy of low-frequency components of dynamical susceptibility χ(q, ωn) have been unraveled as follows; (1) The spin susceptibility at the O(1) sites is much larger than that at the O(2) sites. (2) From the anisotropy in the Knight shift at the O(1) sites, it is shown that the spin density resides predominantly on the in-plane pπ orbitals hybridized with the 4dxy orbitals. (3) From the pronounced anisotropy in (1/T1T) at both sites developed below T*∼130K where the c-axis resistivity shows a metallic behavior, we have found that the low-frequency components of χ(q, ωn) is highly anisotropic in contrast to the uniform spin susceptibility being isotropic. The in-plane components of χ(q, ωn) at the O(1) sites are almost independent of wave number although they are exchange-enhanced, whereas its out-of-plane component is markedly enhanced by interlayer antiferromagnetic (AF) spin fluctuations below T* ∼ 130 K. (4) For the apical O(2) sites on which the p orbitals are hybridized with the 4dxz,yz and pc orbitals on the O() site, the in-plane components of χ(q, ωn) are enhanced by AF-spin fluctuations as well. The AF-spin fluctuations develop as quasiparticles hop coherently along the c-axis below T*. These characteristics of spin fluctuations are suggested to provide a new scenario based on the Hund's coupling as a possible mechanism of spin-triplet p-wave superconductivity in Sr2RuO4, not on analogy with 3He.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Udagawa19982529,

title = {Phonon Raman Scattering Study of K2NiF4 Type Oxide Superconductors},

author = {M Udagawa and H Hata and S Nimori and T Minami and N Ogita and S Sakita and F Nakamura and T Fujita and Y Maeno},

doi = {10.1143/JPSJ.67.2529},

year  = {1998},

date = {1998-01-01},

journal = {Journal of the Physical Society of Japan},

volume = {67},

number = {7},

pages = {2529-2533},

abstract = {La (P1) and apical oxygen (P2) vibrations along the c-axis, which are A1g-symmetry in the tetragonal phase (I4/mmm), have been systematically investigated for K2NiF4-type oxide superconductors; La2CuO4+δ (δ=0, 0.014, 0.063), La1.85Sr0.15CuO4, and Sr2RuO4. For La2CuO4+δ,, with increasing of the excess oxygen concentration (δ), the intensity of P2 decreases exponentially as a function of δ at room temperature. This decreasing can be understood by the shielding effect due to the doped carriers along the c-axis. With decreasing temperature, the intensity of P2 increases for La2CuO4.063 and La1.85Sr0.15CuO4 at low temperature, while La2CuO4 and Sr2RuO4 do not show such anomaly. This might be explained by the decrease of the shielding effect due to the charge confinement along the c-axis. The appearance of the excess oxygen vibration along the c-axis shows that the transition at about 250 K is due to the freezing of the itineracy of the excess oxygen for La2CuO4.063.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tokunaga19971351,

title = {Cu NQR study of spin fluctuation in Ni substituted YBa2Cu3O7},

author = {Y Tokunaga and K Ishida and Y Kitaoka and K Asayama},

doi = {10.1016/S0921-4534(97)00757-0},

year  = {1997},

date = {1997-01-01},

journal = {Physica C: Superconductivity and its Applications},

volume = {282-287},

number = {PART 3},

pages = {1351-1352},

abstract = {From Cu-NQR measurements in YBa2(Cu1-xNix)3O7, all the 63(1/Tl) are found to be on a universal curve, when 1/Tl is plotted against t = T/Tc(x) above Tc. This result indicates that Tc is intimately correlated with the Cu antiferromagnetic spin fluctuation (AFSF) that governs 63(1/Tl). This scaling of 1/Tl to Tc is a direct evidence for the pairing mechanism to be magnetic in origin. The reduction in Tc by the Ni substitution is considered to be due to the decrease in the characteristic energy, ΓQ of AFSF around Q = (π/a,π/a).},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tokunaga199743,

title = {Novel relation between spin-fluctuation and superconductivity in Ni substituted high-Tc cuprate YBa2Cu3O7:Cu NQR study},

author = {Y Tokunaga and K Ishida and Y Kitaoka and K Asayama},

doi = {10.1016/S0038-1098(97)00112-9},

year  = {1997},

date = {1997-01-01},

journal = {Solid State Communications},

volume = {103},

number = {1},

pages = {43-47},

abstract = {From a systematic measurement of the nuclear spin-lattice relaxation rate, 63(1/T1) in YBa2(Cu1-xNix)3O7, it has been found that all the 1/T1 data in the normal state are on a universal curve, when 1/T1 is plotted against t = T/Tc(x) in a T-range of Tc - 400 K and even just below Tc. This experimental results indicates that Tc is intimately correlated with the Cu antiferromagnetic (Cu-AF) spin fluctuation that governs 63(1/T1). This is a direct evidence for the mechanism of the superconductivity being magnetic in origin. The reduction in Tc by the Ni substitution is considered to be due to the decrease in the characteristic energy scale, ΓQ of the Cu-AF spin fluctuation around Q = (π/a, π/a). © 1997 Elsevier Science Ltd.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}