Kenji Ishida

@article{Tokunaga20009707,

title = {Effect of carrier distribution on superconducting characteristics of the multilayered high cuprate study},

author = {Y Tokunaga and K Ishida and Y Kitaoka and K Asayama and K Tokiwa and A Iyo and H Ihara},

doi = {10.1103/PhysRevB.61.9707},

year  = {2000},

date = {2000-01-01},

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

volume = {61},

number = {14},

pages = {9707-9710},

abstract = {We report Cu-NMR studies of the multilayered high-(Formula presented) cuprate (Formula presented) (Cu1234) with (Formula presented) K. In the normal state, the Knight shift (K) and the nuclear spin-lattice relaxation rate (Formula presented) of (Formula presented) give evidence that the inner (Formula presented) planes (IP) are underdoped, whereas the outer ones (OP) are heavily overdoped. In the superconducting (SC) state, both K and (Formula presented) decrease markedly below (Formula presented) K in the IP, whereas in the OP they decrease moderately below (Formula presented) K, but markedly below (Formula presented) K. The unusual NMR results in the OP reveal that the SC gap does not fully develop down to (Formula presented) K. From comparison with a conventional d-wave model, it is shown that the SC gap in the OP increases linearly below (Formula presented) and follows the mean-field type of T dependence below (Formula presented) We propose that these dissimilarities are caused by the large difference of doping levels between the IP and the OP. The bulk SC transition at (Formula presented) K is considered to be triggered by the underdoped IP in Cu1234. © 2000 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kawasaki200014,

title = {Cu-NQR study of magnetism and superconductivity in Ce1+xCu2+ySi2 underpressure},

author = {Y Kawasaki and K Ishida and T Mito and C Thessieu and G -Q Zheng and Y Kitaoka and K Asayama and C Geibel and F Steglich},

doi = {10.1016/S0921-4526(99)01172-2},

year  = {2000},

date = {2000-01-01},

journal = {Physica B: Condensed Matter},

volume = {281-282},

pages = {14-15},

abstract = {In order to investigate the magnetic properties at the vicinity of magnetic to superconducting (SC) phase boundary, we have performed Cu-NQR measurements under hydrostatic pressure (P) on two off-stoichiometric Ce1+xCu2+ySi2. Ce0.99Cu2.02Si2 exhibits the anomalous ground state so-called A-phase, dominated by critical magnetic correlations and affected by a presence of minor SC fraction at ambient P. With increasing P which enhances the Kondo temperature, the fraction of the A-phase is markedly suppressed, but the SC fraction is increased, although Tc stays nearly constant in the range of 1 bar < P < 14.4 kbar. This evidences that the P-induced A- to SC phase change is of first order. In Ce0.975Cu2Si2 which undergoes a static magnetic ordering (SMO) at ambient P below TN ∼ 0.6 K, no superconductivity has been induced up to 19.4 kbar. © 2000 Elsevier Science B.V. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kadono2000322,

title = {Anomalous local magnetic shielding effect at muon site in Sr2.5Ca11.5Cu24O41 and Ce0.99Cu2.02Si2},

author = {R Kadono and A Koda and W Higemoto and K Ohishi and K Kakuta and J Akimitsu and K Ishida and Y Kitaoka and C Geibel and F Steglich},

doi = {10.1016/S0921-4526(00)00402-6},

year  = {2000},

date = {2000-01-01},

journal = {Physica B: Condensed Matter},

volume = {289-290},

pages = {322-325},

abstract = {We present that the time structure of ZF- and LF-μSR spectra in the magnetic phase of Sr2.5Ca11.5Cu24O41 and in the A-phase of Ce0.99Cu2.02Si2 shares a number of common features. In particular, the magnitude of local magnetic field at the muon site estimated from ZF-μSR is seemingly far smaller than that estimated by LF-quenching experiment. As a microscopic model of such an anomalous local magnetic shielding, we discuss the possibility of muon-induced local magnetism due to the magnetic instability of frustrated spin systems near the quantum critical point.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tokunaga2000663,

title = {Pseudogap and superconducting fluctuations in Bi2Sr2CaCu2O8+y probed by 63Cu NMR},

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

doi = {10.1016/S0921-4526(99)02328-5},

year  = {2000},

date = {2000-01-01},

journal = {Physica B: Condensed Matter},

volume = {284-288},

number = {PART I},

pages = {663-664},

abstract = {We report temperature dependence of the Gaussian component of spin-echo decay rate (1/T2G) in single crystals Bi2Sr2CaCu2O8+y(Bi2212). We found that 1/T2G starts to decrease at a certain temperature, Tc*, which is higher than Tc and lower than the pseudogap temperature, T*, suggesting the formation of local Cooper pairing without global phase coherency. Based on our NMR results, we develop the phase diagram in the Bi2212 system which includes three crossover temperatures, TmK, T* and Tc*. © 2000 Elsevier Science B.V. All rights reserved.},

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{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{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{Tokunaga1999473,

title = {Carrier distribution and superconductivity in multilayer high-Tc cuprates proved by 63Cu NMR},

author = {Y Tokunaga and H Kotegawa and K Ishida and G -Q Zheng and Y Kitaoka and K Tokiwa and A Iyo and H Ihara},

year  = {1999},

date = {1999-01-01},

journal = {Journal of Low Temperature Physics},

volume = {117},

number = {3-4},

pages = {473-477},

abstract = {The carrier distribution among the inequivalent CuO2 planes in multilayer cuprates is investigated by 63Cu Knight shift measurement with varying the carrier concentration, δ and the number of CuO2 plane in a unit cell, n. We found that 70 (60)% of total carriers are doped selectively into two outer CuO2 planes in n = 3 (4). This indicates resultantly that the inhomogeneity of carrier distribution increases with increasing δ and n in multilayer cuprates.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ihara199967,

title = {Creation of the best performance high-Tc superconductor based on Cu-1234},

author = {H Ihara and Y Tanaka and A Iyo and H Kito and N Terada and M Tokumoto and K Ishida and Y Sekita and H Yamamoto and K Hayashi and N A Khan and A Sundaresan and J Nie and T Kojima and E Harashima and Y Ishiura and F Tateai and M Kawamura},

year  = {1999},

date = {1999-01-01},

journal = {Denshi Gijutsu Sogo Kenkyusho Iho/Bulletin of the Electrotechnical Laboratory},

volume = {63},

number = {1},

pages = {67-75},

abstract = {The purpose of this project is to create the best performance superconductor on the basis of our original Cu1234(CuBa2Ca3Cu4O12-y) superconductor. Its best performance superconductor will be realized by the modification of superconducting wave function(MSWF) and application of new preparation techniques of thin films. The MSWF leads to the enhancement of coherence length along the c-axis and transformation from d-wave to(d+is)-wave, and then low superconducting anisotropy. The thin film techniques are APE(amorphous phase epitaxy) method and SAE(self assembling epitaxy) method by using structure stabilizer such as Tl. The best superconductor with long coherence length, low anisotropy, high Tc, high Jc and high Hirr will be realized for wire and Josephson junction and microwave device application at 77 K.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kawasaki199977,

title = {Ru-NMR study of pseudo-metamagnetic transition in CeRu2Si2},

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

doi = {10.1016/S0921-4526(98)00622-X},

year  = {1999},

date = {1999-01-01},

journal = {Physica B: Condensed Matter},

volume = {259-261},

pages = {77-78},

abstract = {Ru-NMR study of CeRu2Si2 up to a magnetic field H = 15.5 T has revealed that the dramatic evolution in heavy-fermion (HF) state takes place through a pseudo-metamagnetic transition at HM ̃ 7.8 T. The HF state in H < 3 T is characterized by the T1T = constant relation below 8 K, whereas the 1/T1T at HM continues to increase upon cooling to 1.4K, suggesting a very low characteristic energy. As if increases above HM, the value of 1/T1T = constant being valid far below 8 K is successively reduced with much smaller values than that for H < 3 T. Appearance of the peak in 1/T1T at higher T points to an unusual renormalization process for 4f electrons to form the spin-polarized Fermi liquid state. © 1999 Elsevier Science B.V. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mukuda199912279,

title = {Spin fluctuations in the ruthenium oxides RuO2, SrRuO3, CaRuO3, and Sr2RuO4 probed by Ru NMR},

author = {H Mukuda and K Ishida and Y Kitaoka and K Asayama and R Kanno and M Takano},

doi = {10.1103/PhysRevB.60.12279},

year  = {1999},

date = {1999-01-01},

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

volume = {60},

number = {17},

pages = {12279-12285},

abstract = {By means of Ru NMR, magnetic properties in three-dimensional (3D) perovskites SrRuO3 (ferromagnet) and CaRuO3 (exchange enhanced paramagnet) were investigated and compared with those in the two-dimensional (2D) layered perovskite Sr2RuO4 (superconductor), RuO2, and Ru metal (Pauli paramagnet). We found that 4d-spin contributions in the Knight shift and 101(1/T1) of Ru are predominant in SrRuO3, CaRuO3, and Sr2RuO4, but not in nonmagnetic RuO2 and Ru metal. The experimental results that a Stoner factor for CaRuO3 is close to 1 and that a correlation factor estimated from modified-Korringa behavior of Ru-T1 is much less than 1 indicate that CaRuO3 is a nearly ferromagnetic (FM) metal dominated by low-frequency and long-wavelength components of the spin fluctuations (SF). Even though the Stoner factor for Sr2RuO4 also indicates the closeness to the ferromagnetism, the SF in Sr2RuO4 are different from those in CaRuO3. The results combined with the previous 17O NMR study in Sr2RuO4 indicate that the in-plane low-frequency components of SF are exchange enhanced without any significant q dependence due to 2D electronic character (2D nearly FM), while the out-of-plane low-frequency component of SF shows the existence of antiferromagnetic (AFM) SF between layers at low temperature. We propose that this evolution from 3D to 2D nearly FM SF is relevant to the onset of spin-triplet superconductivity in Sr2RuO4. The 2D nearly FM SF in the in-plane 4dxy-pπ band may play a significant role for the stabilization of parallel spin pairing state within the basal plane among various representations of spin-triplet order parameter in Sr2RuO4. © 1999 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ohsugi19991040,

title = {Impurity effect of the spin ladder system SrCu2O3},

author = {S Ohsugi and Y Kitaoka and Y Tokunaga and K Ishida and M Azuma and Y Fujishiro and M Takano},

doi = {10.1016/S0921-4526(98)00879-5},

year  = {1999},

date = {1999-01-01},

journal = {Physica B: Condensed Matter},

volume = {259-261},

pages = {1040-1041},

abstract = {The existence of the antiferromagnetic (AF) long-range order in nonmagnetic impurity-doped ladder system Sr(Cu1-xMx)2O3 (M = Zn, Ni) with x = 0.01 and 0.02 has been confirmed from the observations of the broadened Cu nuclear quadrupole resonance (NQR) spectrum due to the hyperfine (internal) field and the drastic change of the Gaussian spin-echo decay rate, T2G-1, at 1.4 K. From Cu NMR and NQR results, we propose a possible spin configuration of the AF staggered moments in the ordered state. © 1999 Elsevier Science B.V. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ohsugi19994181,

title = {Impurity-induced staggered polarization and antiferromagnetic order in spin-1/2 Heisenberg two-leg ladder compound SrCu2O3: Extensive Cu NMR and NQR studies},

author = {S Ohsugi and Y Tokunaga and K Ishida and Y Kitaoka and M Azuma and Y Fujishiro and M Takano},

doi = {10.1103/PhysRevB.60.4181},

year  = {1999},

date = {1999-01-01},

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

volume = {60},

number = {6},

pages = {4181-4190},

abstract = {We report characteristics of impurity-induced staggered polarization (IISP) and antiferromagnetic long-range order (AF-LRO) in the gapped spin-1/2 Heisenberg two-leg ladder compound SrCu2O3 (Sr123). We have carried out comprehensive NMR and NQR investigations on three impurity-doped systems, Sr(Cu1−xMx)2O3(M=Zn, Ni) with x < 0.02 and Sr1−xLaxCu2O3 with x<0.03. Either the Zn or Ni impurity that is nonmagnetic depletes a single spin on the ladders, whereas the La impurity is believed to dope electrons onto the ladders. The width of the Lorentzian Cu NMR spectrum increases with the increase in impurity content x and follows the Curie-like temperature (T) dependence as W/T. The W's for the Zn- and Ni-doped samples (M doping) are larger than for the La-doped one (La doping). The NMR spectra were fit by assuming that unpaired spin S0=1/2 induced next to impurity on the rung for the Zn and Ni doping (S0=1/4 for the La doping) creates the staggered spin polarization along the leg, which decreases exponentially from S0. In Sr123, an instantaneous spin-correlation length ξ0 was theoretically predicted as ξ0/a3−8, where a is the lattice spacing between the Cu sites along the leg. However, a correlation length ξs/a estimated from the IISP along the leg was found to be much longer than ξ0/a in x=0.001 and 0.005. The notable result is that ξs/a that was found to be T independent is scaled to mean distances DAV=1/(2x) between the Zn and Ni impurities and DAV=1/x between the La impurities. When DAV=500 for x=0.001 (Zn doping), ξs/a50 is estimated. The significantly broadened NQR spectrum has provided unambiguous evidence for the AF-LRO in the Zn and Ni doping (x=0.01 and 0.02). Rather uniform AF moments at the middle Cu sites between the impurities are estimated to be about 0.04μB at 1.4 K along the a axis. By assuming that exponential decay constants of AF moments are equivalent to ξs/a's for the IISP, the size of an AF moment next to the impurity is deduced as SAF1/4. We propose that these exponential distributions of IISP and AF moments along the two-leg suggest that an interladder interaction is in a weakly coupled quasi-one-dimensional (WC-Q1D) regime. The formula of TN=J0exp(−DAV/(ξs/a)) based on the WC-Q1D model explains TN(exp)=3 K (x=0.01) and 5.8 K (x=0.02) quantitatively and predicts to be as small as TN=0.09 K for x=0.001 using J0=2000 K. On the other hand, there is no evidence of AF-LRO for the La doping (x=0.02 and 0.03) down to 1.4 K, nevertheless their ξs/a's are almost equivalent to those in the Zn and Ni doping (x=0.01 and 0.02). We remark that the Q1D-IISP is dramatically enhanced by the interladder interaction even though so weak, once the impurity breaks up the quantum coherence in the short-range resonating valence bond (RVB) state with the gap. On the one hand, we propose that TN is determined by a strength of the interladder interaction and a size of S0. © 1999 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida1999678,

title = {Crossover behavior from magnetism to superconductivity in CexCu2Si2},

author = {K Ishida and Y Kawasaki and K Tabuchi and K Kashima and Y Kitaoka and K Asayama and C Geibel and F Steglich},

doi = {10.1016/S0921-4526(98)01035-7},

year  = {1999},

date = {1999-01-01},

journal = {Physica B: Condensed Matter},

volume = {259-261},

pages = {678-680},

abstract = {Cu-NQR studies have been performed to clarify the ground-state characteristics in a series of CexCu2Si2 system. It was found that the ground state evolves from magnetically ordered state at x = 0.975 to heavy-electron superconducting state at x = 1.025. At the border between the two phases (x = 0.99), the novel magnetic character survives even at the lowest temperature. We propose that this magnetic state may be a dynamical SDW state oscillating with finite frequencies comparable to Cu-NQR frequency (∼3 MHz). © 1999 Elsevier Science B.V. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida19995353,

title = {Evolution from magnetism to unconventional superconductivity in a series of CexCu2Si2 compounds probed by Cu NQR},

author = {K Ishida and Y Kawasaki and K Tabuchi and K Kashima and Y Kitaoka and K Asayama and C Geibel and F Steglich},

doi = {10.1103/PhysRevLett.82.5353},

year  = {1999},

date = {1999-01-01},

journal = {Physical Review Letters},

volume = {82},

number = {26},

pages = {5353-5356},

abstract = {We report on the basis of Cu-NQR measurements that the ground state in a series of CexCu2Si2 compounds evolves from a magnetically ordered phase at x = 0.975 to a heavy-electron superconducting (SC) phase at x = 1.025. We have found that the sample of x = 0.99 does not exhibit any trace of magnetic phase transition down to 0.012 K. Slow magnetic fluctuations with low frequencies comparable to the NQR frequency develop rapidly below Tm∼1.2 K. This unusual “critical magnetic phase” can coexist with the SC phase. For the samples of x = 1.00 and 1.025 such a state is expelled by the onset of the SC state. © 1999 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida1999511,

title = {NMR study of high-Tc superconductors and related materials},

author = {K Ishida and Y Tokunaga and Y Kitaoka and G -Q Zheng and K Magishi and H Mukuda and H Tou and T Mito and K Asayama},

doi = {10.1016/S0921-4526(98)01015-1},

year  = {1999},

date = {1999-01-01},

journal = {Physica B: Condensed Matter},

volume = {259-261},

pages = {511-516},

abstract = {Recent NMR measurements on high-Tc and related material Sr2RuO4 by the Osaka group are reviewed. The following results are presented: (1) Study of YBa2Cu3O7 + Ni has revealed that the attractive force is spin in origin. (2) Analysis of T1, T2 and Knight shift (K) in various high-Tc materials supports the antiferromagnetic spin-fluctuation mediated superconducting model. (3) Temperatures at which a pseudogap starts to open obtained by 1/T1T, dK/dT, photoemission and resistivity agree with each other in the Bi2Sr2CaCu2O8+δ system. (4) 17O Knight shift measurements in the related material Sr2RuO4 suggests that a triplet pairing is realized in this compound as in the heavy-fermion superconductor UPt3. © 1999 Published by Elsevier Science B.V. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tokunaga1999571,

title = {NMR study of magnetic excitations and pseudogap in HgBa2Ca3Cu4Oy},

author = {Y Tokunaga and K Ishida and K Magishi and S Ohsugi and G -Q Zheng and Y Kitaoka and K Asayama and A Iyo and K Tokiwa and H Ihara},

doi = {10.1016/S0921-4526(98)01066-7},

year  = {1999},

date = {1999-01-01},

journal = {Physica B: Condensed Matter},

volume = {259-261},

pages = {571-572},

abstract = {We report systematic Cu-NMR study on HgBa2Ca3Cu4O10+y with Tc = 123K comprising respective 4-fold and 5-fold two CuO2 planes surrounded by square and pyramidal oxygens. Possible structure and temperature dependence of the normal-state pseudogap have been extracted from the steep decrease of the spin contribution in the Knight shift, Ks below TK* ∼ 220 K. By assuming the linear increase of a size of pseudogap between TK* and Tc with the dx2-y2 symmetry, the T-dependence of Ks/Kn in both 4- and 5-fold is reproduced below TK*. © 1999 Elsevier Science B.V. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida1999559,

title = {Pseudogap behavior in single crystals of Bi2Sr2CaCu2O8+δ},

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

doi = {10.1016/S0921-4526(98)01036-9},

year  = {1999},

date = {1999-01-01},

journal = {Physica B: Condensed Matter},

volume = {259-261},

pages = {559-561},

abstract = {In under- and optimally doped Bi2Sr2CaCu2O8 (Bi2212), we found a characteristic temperature TK*, below which the spin part of Knight shift Ks starts to decrease steeply and extrapolates to zero at T > 0. TK* is in good agreement with the temperatures at which the pseudogap starts to open in the quasiparticle density of states (DOS) at the Fermi level, and A* at which 1/T1T has a broad peak. We propose that the spin-gap behavior observed in NMR measurements has the same origin as the pseudogap in the quasiparticle DOS. © 1999 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{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{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{Ishida1997R505,

title = {Anisotropic pairing in superconducting Ru NMR and NQR studies},

author = {K Ishida and Y Kitaoka and K Asayama and S Ikeda and S Nishizaki and Y Maeno},

doi = {10.1103/PhysRevB.56.R505},

year  = {1997},

date = {1997-01-01},

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

volume = {56},

number = {2},

pages = {R505-R508},

abstract = {Ru NMR and nuclear quadrupole resonance studies are reported on single-crystal (Formula presented)0.7 K) with the same layered perovskite structure as (Formula presented). The Pauli spin susceptibility deduced from the Ru Knight shift is found to be largely enhanced by a factor of (Formula presented)5.4 as compared with the value from the band calculation. In the superconducting state, the nuclear spin-lattice relaxation rate (Formula presented) exhibits a sharp decrease with no coherence peak just below (Formula presented) and the (Formula presented)=constant behavior well below (Formula presented) suggesting that the anisotropic pairing state is realized as in heavy-fermion and high-(Formula presented) superconductors. © 1997 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kitaoka1997210,

title = {Spin fluctuation and unconventional pairing in Sr2RuO4},

author = {Y Kitaoka and K Ishida and K Asayama and S Ikeda and S Nishizaki and Y Maeno and K Yoshida and T Fujita},

doi = {10.1016/S0921-4534(97)00202-5},

year  = {1997},

date = {1997-01-01},

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

volume = {282-287},

number = {PART 1},

pages = {210-213},

abstract = {Sr2RuCO4 with Tc =0.7 K with the same layered perovskite structure as La2CuO1 is the exchange-enhanced Pauli paramagnet with the two dimensional (2D) electronic structure. The superconductivity of has been found to be unconventional from the nuclear relaxation behavior exhibiting a sharp decrease with no coherence peak just below Tc and the T1T=constant behavior well below Tc. In comparison with the high-Tc Bi2Sr2CaCu2O8+y (Bi2212) and the 3D analogue of exchange-enhanced Pauli paramagnet CeCo2, the similarity and dissimilarity are presented on the normal and superconducting states.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida19971369,

title = {Anisotropic pairing in superconducting Sr2RuO4 (Tc ∼0.7K)},

author = {K Ishida and Y Kitaoka and K Asayama and S Ikeda and S Nishizaki and Y Maeno and K Yoshida and T Fujita},

doi = {10.1016/S0921-4534(97)00770-3},

year  = {1997},

date = {1997-01-01},

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

volume = {282-287},

number = {PART 3},

pages = {1369-1370},

abstract = {Ru NQR study in single crystals of Sr2RuO4 (Tc ∼ 0.7K) has been carried out to investigate a superconducting pairing state. In the superconducting state, 1/T1 exhibits a sharp decrease with no coherence peak just below Tc and the T1T=constant behavior well below Tc, suggesting that the anisotropic pairing state is realized as in high-Tc and heavy-fermion superconductors.},

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}

}

@article{Ishida1997383,

title = {Cu NQR study of magnetic correlation and superconductivity in a series of Ce1+xCu2+ySi2},

author = {K Ishida and Y Kitaoka and K Kashima and K Asayama and C Geibel and F Steglich},

doi = {10.1016/S0921-4526(96)00729-6},

year  = {1997},

date = {1997-01-01},

journal = {Physica B: Condensed Matter},

volume = {230-232},

pages = {383-386},

abstract = {The anomalous magnetic and superconducting properties in a series of non-stoichiometric Ce1 + xCu2 + ySi2 samples have been investigated by the Cu NQR. In a CeCu2.05Si2 sample regarded as the best quality to date, the superconducting state is within the H-T phase diagram embedded in the unusual A-phase dominated by critical magnetic fluctuations, whereas this A-phase is markedly suppressed in the off-stoichiometric compounds, Ce1.025Cu2Si2 and CeCu2.2Si2 with lower Tc. No difference in the relaxation behavior in the the superconducting state was observed between both type of samples.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mito19971365,

title = {NMR study in single-layered high-Tc compounds near the antiferromagnetic insulator phase boundary},

author = {T Mito and K Ishida and Y Kitaoka and K Asayama and H Eisaki and S Uchida},

doi = {10.1016/S0921-4534(97)00767-3},

year  = {1997},

date = {1997-01-01},

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

volume = {282-287},

number = {PART 3},

pages = {1365-1366},

abstract = {In order to unravel the nature of spin correlations in the vicinity of the transition between antiferromagnetic (AF) and superconducting phases, 63Cu NMR measurements have been carried out for the 8%-Sr doped La2-xSrxCuO4 (LSCO) and hole-reduced Bi2Sr2CuO4 (Bi2201) with Tc = 0 K. It was found that Bi2201 exhibits neither superconductivity nor long-range order from the NMR experiments. 63(1/T1T) in B12201 shows successive decrease down to 100 K, suggesting the presence of the pseudo spin-gap in contrast to its significant increase in 8%-LSCO.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida1997304,

title = {59Co NQR study in superconducting CeCo2},

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

doi = {10.1016/S0921-4526(97)00183-X},

year  = {1997},

date = {1997-01-01},

journal = {Physica B: Condensed Matter},

volume = {237-238},

pages = {304-306},

abstract = {We have performed 59Co NQR study in superconducting CeCo2 with Tc ∼ 1.4 K in order to investigate the superconducting property. Nuclear spin-lattice relaxation rate of Co, 1/T1 was measured down to 150 mK. 1/T1 is proportional to temperature (T) in the normal state, and decreases exponentially in the superconducting state with the Hebel-Slichter peak just below Tc. T-dependence of 1/T1 in the superconducting state is a typical feature of s-wave superconductivity with 2Δ/kBTc ∼ 2.26, which is remarkably smaller than 3.5 in the BCS superconductor.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Magishi19971115,

title = {63Cu NMR study on spin ladder compounds Sr14-xCaxCu24O41 (x = 9, 11.5)},

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

doi = {10.1016/S0921-4534(97)00671-0},

year  = {1997},

date = {1997-01-01},

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

volume = {282-287},

number = {PART 2},

pages = {1115-1116},

abstract = {63Cu NMR measurements for the ladder sites on single crystals Sr14-xCaxCu24O41 (x = 9, 11.5), which consist of simple chains and 2-leg ladders of Cu2+ ions, have been carried out at f = 125.1 MHz for H ∥ b-axis. From respective measurements of the Knight shift and the nuclear spin-lattice relaxation rate, 1/T1, the spin gap in the ladder has been found to be as large as Δ = 250 K (260 K) and 340 K (360 K) for x = 11.5 (x = 9), respectively.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida19971367,

title = {Cu NQR study in Zn- and Ni-doped La1.825Sr0.175CuO4},

author = {K Ishida and T Tanaka and H Yamanaka and T Mito and Y Tokunaga and K Yoshida and K Yamazoe and S Ohsugi and Y Kitaoka and K Asayama},

doi = {10.1016/S0921-4534(97)00769-7},

year  = {1997},

date = {1997-01-01},

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

volume = {282-287},

number = {PART 3},

pages = {1367-1368},

abstract = {We have investigated an influence of Zn- and Ni-doping at CuO2 plane in various high-Tc compounds. In optimum-doped LSCO, La1.825Sr0.175CuO4, magnetic Ni as well as nonmagnetic Zn induce a large residual density of states (RDOS) in the superconducting state. The induction of RDOS by slight Zn-doping is considered to be a common feature in optimum-doped high-Tc compounds.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ihara19971973,

title = {How to make superconducting-anisotropy least in high-Tc cuprate superconductors},

author = {H Ihara and A Iyo and K Tanaka and K Tokiwa and K Ishida and N Terada and M Tokumoto and Y Sekita and T Tsukamoto and T Watanabe and M Umeda},

doi = {10.1016/S0921-4534(97)01057-5},

year  = {1997},

date = {1997-01-01},

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

volume = {282},

number = {PART 4},

pages = {1973-1974},

abstract = {The guiding principles to reduce superconducting-anisotropy were derived for high-Tc cuprate superconductors. Based on the principles, we have attained the least superconducting-anisotropy γ=1.6 for a Cu-based CuBa2Ca3Cu4O12-y (Cu-1234) superconductor. Further lower superconducting-anisotropy has been proposed for Cu-1245 (γ=1.3) and Cu-1256 (γ=1.0) Cu-based superconductors.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida19961093,

title = {Ru NMR and NQR Studies in Superconducting Sr2RuO4 with Tc = 0.7K},

author = {K Ishida and Y Kitaoka and K Asayama and S Ikeda and Y Maeno and T Fujita},

year  = {1996},

date = {1996-01-01},

journal = {Czechoslovak Journal of Physics},

volume = {46},

number = {SUPPL. 2},

pages = {1093-1094},

abstract = {Ru NMR and NQR studies have been made in the superconducting single crystal Sr2RuO4 (Tc = 0.7K) in order to investigate an electronic state in the RuO2 plane. It has been found that the T1T and the Knight shift stay constantly between 1.4 and 4.2 K, which allows us to estimate the Stoner factor, α and the enhancement factor of the Korringa product K(α) to be 0.92 and 1, respectively. From these results, it is shown that Sr2RuO4 is characterized by dominant ferromagnetic fluctuations and two-dimensional(2-D) electronic structure.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tokunaga19961139,

title = {Coexistence of magnetic ordering induced by Ni spins and superconductivity in Ni-substituted YBa2Cu3O7-Cu NQR study-},

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

doi = {10.1007/BF02583877},

year  = {1996},

date = {1996-01-01},

journal = {Czechoslovak Journal of Physics},

volume = {46},

number = {SUPPL. 2},

pages = {1139-1140},

abstract = {From the Cu NQR measurements ill tlae superconducting state of Ni-substituted YBa2(Cu1-xNix)3O7, it has been found that the nuclear spin-lattice relaxation rate, 1/T1 and the spin echo decay rate, l/T2 of 63Cu are largely enhanced around TM = 2.5 and 3.5 K for 7 and 10% Ni doping, respectively. Below TM, the Cu NQR spectrum has revealed the presence of distributed internal fields at Cu nuclei in the CuO2 plane with a maximum value of ~2.5 kOe. From these results, the magnetic ordering is concluded to take place by the indirect exchange coupling among Ni moments with S = 1/2 mediated by the antiferromagnetic Cu spin polarization around Q = (π/a, π/a) in the CuO2 plane. We propose that the superconductivity coexist with the magnetic ordering due to the d wave nature with node line around Q = (π/a, π/a).},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mito19961145,

title = {Spin correlation in superconducting La1.92Sr0.08CuO4 near the antiferromagnetic insulator phase boundary},

author = {T Mito and Y Kitaoka and T Tanaka and K Ishida and K Asayama},

year  = {1996},

date = {1996-01-01},

journal = {Czechoslovak Journal of Physics},

volume = {46},

number = {SUPPL. 2},

pages = {1145-1146},

abstract = {In order to unravel tile nature of spin correlation in the vicinity of the antiferromagnetic (AF) phase boundary, the 63Cu nuclear spin lattice relaxation rate, 63(1/T1), has been measured for the 8%-Sr doped superconducting (SC) La2-xSrxCuO4 (LSCO) by Cu NMR and NQR techniques. The temperature dependence of 63(1/T1T) has revealed a continuous increase down to Tc without the spin pseudogap behavior observed in underdoped YBa2Cu3O6+x and YBa2Cu4O8.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Asayama19963187,

title = {NMR of high Tc superconductors},

author = {K Asayama and Y Kitanka and G -Q Zheng and K Ishida and K Magishi and T Mito and Y Tokunaga},

doi = {10.1007/BF02548129},

year  = {1996},

date = {1996-01-01},

journal = {Czechoslovak Journal of Physics},

volume = {46},

number = {SUPPL. 6},

pages = {3187-3194},

abstract = {Results of our NMR measurements of high Tc superconductors are reviewed. From systematic measurements of NQR frequency, Knight shift, nuclear spin lattice relaxation rate and nuclear transverse relaxation rate over a wide hole concentration range from light to heavy doped compounds together with the impurity and pressure effect, following results are concluded. The numbers of the holes at the respective sites of Cu and O site in the CuO2 plane govern the several physical properties of the system. There are optimum values of these hole numbers to produce highest Tc. The superconducting properties are well explained consistently by the d-wave pairing model. Tc is found to be correlated intimately with the antiferromagnetic spin fluctuation parameters that governs the nuclear relaxation. The mechanism for the superconductivity is magnetic in origin.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Asayama1996478,

title = {NMR study of high-TC superconductors},

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

doi = {10.1016/0921-4526(96)00153-6},

year  = {1996},

date = {1996-01-01},

journal = {Physica B: Condensed Matter},

volume = {223-224},

number = {1-4},

pages = {478-483},

abstract = {Recent NMR study of high-TC superconductors carried out by Osaka group is reviewed. NQR frequency vQ, Knight shift K, T1 of 63Cu and 17O were measured over a wide hole doping range from light-to heavy-doped systems, LSCO, YBCO, HBCCO, BSCCO, TBCCO and TBCO, together with impurity and pressure effect. By analysing vQ, K and T1, the local hole numbers of Cu and O at the CuO2 plane, n(Cu) and n(O) the relative magnitude of the uniform susceptibility, χ0 and the low-frequency component of the antiferromagnetic spin fluctuations (AFSF), χQ/Γ (χQ is the staggered susceptibility and Γ is the characteristic energy of the spin fluctuation at q = 0) are obtained. The relation between n(Cu), n(O) and χQ, χQ/Γ, TC, etc. were discussed. There are optimum values of n(Cu)/2n(O) and n(Cu) + 2n(O) to give maximum TC. The NMR results in the superconducting state are well-explained by d-wave pairing model. The result is consistent with the AFSF mediated superconducting model.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Asayama1996221,

title = {NMR studies of high Tc superconductors},

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

doi = {10.1016/0079-6565(95)01025-4},

year  = {1996},

date = {1996-01-01},

journal = {Progress in Nuclear Magnetic Resonance Spectroscopy},

volume = {28},

number = {3-4},

pages = {221-253},

keywords = {},

pubstate = {published},

tppubtype = {article}

}