石田 憲二

@article{Ishida1996793,

title = {Ru NMR and NQR Studies in CeRu2},

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

doi = {10.1515/zna-1996-5-673},

year  = {1996},

date = {1996-01-01},

journal = {Zeitschrift fur Naturforschung - Section A Journal of Physical Sciences},

volume = {51},

number = {5-6},

pages = {793-796},

abstract = {We have carried out Ru NMR and NQR measurements in superconductor CeRu2 having Tc = 6.1 K in the temperature range of 1.3- 30 K. From the 99Ru NMR in 10.2 T above Hc2},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida1996371,

title = {Spin correlations in the normal state of a Bi2Sr2CaCu2O8 single crystal},

author = {K Ishida and Y Kitaoka and K Asayama and K Kadowaki and T Mochiku},

doi = {10.1016/0921-4534(95)00756-3},

year  = {1996},

date = {1996-01-01},

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

volume = {263},

number = {1-4},

pages = {371-374},

abstract = {The Gaussian component of the spin-echo decay rate, 1/T2G of 63Cu mediated by magnetic fluctuations, has been measured in the normal state on single crystal Bi2Sr2CaCu2O8 (Bi2212). The temperature dependence of 1/T2G bears a resemblance to that of 1/T1T, exhibiting a peak at around 140 K. It has been found that the T-dependence of 1/T2G quite contrasts with those in the underdoped compounds such as YBa2Cu3O6.63 and YBa2Cu4O8, although the T-dependences of the Knight shift and 1/T1T seem to be analogous to each other. From the analyses taking all sets of data, such as 1/T2G, the spin susceptibility and 1/T1T, the character of spin fluctuations in Bi2212 is deduced to be similar to that in YBa2Cu3O7, which is considered to be at optimum hole doping, although the T-dependences of 1/T1T, 1/T2G and Ks(T) are seemingly different from each other.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida1996531,

title = {Al NMR Probe of Local Moments Induced by an Al Impurity in High-Tc Cuprate La1.85Sr0.15CuO4},

author = {K Ishida and Y Kitaoka and K Yamazoe and K Asayama and Y Yamada},

doi = {10.1103/PhysRevLett.76.531},

year  = {1996},

date = {1996-01-01},

journal = {Physical Review Letters},

volume = {76},

number = {3},

pages = {531-534},

abstract = {27Al and 63Cu NMR measurements in 3% Al-doped La1.85Sr0.15CuO4 (LSCO) have revealed that the T dependences of the Knight shift, 27K(T), and the nuclear-spin-lattice relaxation rate, 27(1/T1), are dominated by local moments induced at neighboring Cu sites by the Al impurity. These experiments prove that spin fluctuation of induced moments is mainly due to the local spin-exchange coupling, Jsd, with conducting holes. This novel T dependence of 27(1/T1) has led to a reliable estimation of Jsd = 0.055eV, and the extraction of the Tc Δ Tc = 0.62K/Al% based on the magnetic pair-breaking scheme, which is by more than 1 order of magnitude smaller than the experimental value of ΔTc = 23K/Al%. © 1996 American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida19962341,

title = {93Nb NQR Study in Layered Superconducting 2H-NbSe2},

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

doi = {10.1143/JPSJ.65.2341},

year  = {1996},

date = {1996-01-01},

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

volume = {65},

number = {7},

pages = {2341-2342},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida1996329,

title = {Antiferromagnetic Nuclear Resonance of Cu in Infinite-Layer Compounds, SrCuO2 and Ca0.9Sr0.1CuO2 -Comparison between Hyperfine Coupling Constant in a CuO2 Plane and in a Spin-Ladder System-},

author = {K Ishida and Yo. Tokunaga and Y Kitaoka and K Asayama and M Azuma and Z Hiroi and M Takano},

doi = {10.1143/JPSJ.65.329},

year  = {1996},

date = {1996-01-01},

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

volume = {65},

number = {1},

pages = {329-330},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Matsumoto1996R11942,

title = {Competition between the singlet-spin liquid state and the magnetic ground state in a two-chain spin-½ antiferromagnetic ladder compound LaC: A NMR study},

author = {S Matsumoto and Y Kitaoka and K Ishida and K Asayama and Z Hiroi and N Kobayashi and M Takano},

doi = {10.1103/PhysRevB.53.R11942},

year  = {1996},

date = {1996-01-01},

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

volume = {53},

number = {18},

pages = {R11942-R11945},

abstract = {The magnetic characteristics of LaCu(Formula presented) comprising an antiferromagnetic two-chain spin-½ ladder have been investigated by (Formula presented) NMR measurements. The ground state of this compound was suggested from susceptibility measurements to be the singlet-spin liquid state. The present experiments have, however, revealed that LaCu(Formula presented) is not in such a spin-liquid state, but rather a magnetic ordering takes place below (Formula presented) K as evidenced by the large enhancement of the nuclear spin-lattice relaxation rate, ((Formula presented)) and of the spin-echo decay rate, (Formula presented) leading to the disappearance of the Cu NMR signal. This magnetic ordered state has been found to be suppressed by substituting Sr for La by 5%, i.e., by hole doping. © 1996 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida19962827,

title = {Spin correlation and spin gap in quasi-one-dimensional spin-1/2 cuprate oxides: A NMR study},

author = {K Ishida and Y Kitaoka and Y Tokunaga and S Matsumoto and K Asayama and M Azuma and Z Hiroi and M Takano},

doi = {10.1103/PhysRevB.53.2827},

year  = {1996},

date = {1996-01-01},

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

volume = {53},

number = {5},

pages = {2827-2834},

abstract = {The Cu-NMR nuclear relaxation rate, (Formula presented)(1/(Formula presented)) and Gaussian spin-echo decay rate, (Formula presented)(1/(Formula presented)) have been measured in order to investigate the low-energy spin dynamics in the quasi-one-dimensional (1D) spin-1/2 antiferromagnetic (AF) cuprates such as (Formula presented)(Formula presented) with single chain, (Formula presented) at ambient pressure (AP) with zigzag chain coupled by weak ferromagnetic exchange interaction, (Formula presented)(Formula presented) and (Formula presented)(Formula presented)(Formula presented) comprising of two- and three-leg ladder, respectively with isotropic AF exchange interaction along and between chains. In (Formula presented)(Formula presented), 1/(Formula presented) stays constantly close to the 3D magnetic ordering temperature, (Formula presented)∼10 K, dominated by dissipation of overdamped spinons gas as shown theoretically by Sachdev. By contrast, in AP-(Formula presented), 1/(Formula presented) below around 100 K decreases markedly down to the 3D magnetic ordering temperature, (Formula presented)∼3 K, providing a signature that the frustrated ferromagnetic interaction between CuO zigzag chains makes the spin gap open. In the spin-1/2 ladder compounds of (Formula presented)(Formula presented) and (Formula presented)(Formula presented)(Formula presented) consisting of two- and three-leg, respectively, the former was demonstrated in the literatures to have the spin gap amounting to a half of AF exchange constant, J/2 where J=1300 K. For the latter, on the other hand, the magnetic coherence length, ξ(T) grows up according to ξ(T)∼1/(T-θ) and as a result, the magnetic ordering emerges around 50-60 K accompanying the divergence of 1/(Formula presented). In the compounds composed of single and triple chains, it is shown that there is no analog of renormalized classical region identified in the 2D spin-1/2 cuprate such as (Formula presented)(Formula presented), but the spin dynamics is in the quantum critical regime over wide T range due to the finite size of chains, even though the 3D magnetic ordering takes place at very low temperature. This is considered because the spin correlators have a power-law decay only along the chain, but between chains is limited to the number of chains in contrast to the 2D square lattice. For the compounds with two chains, the exchange coupling between chains leads to the formation of spin gap phase regardless of whether its sign is antiferromagnetic or ferromagnetic. A result on doping into the two-leg ladder, (Formula presented)(Formula presented) is argued in terms of the localization effect of carriers. © 1996 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida19951915,

title = {Cu NMR study of organic conductor DCNQI-Cu system},

author = {K Ishida and Y Kitaoka and H Masuda and K Asayama and T Takahashi and A Kobayashi and R Kato and H Kobayashi},

doi = {10.1016/0379-6779(94)03105-F},

year  = {1995},

date = {1995-01-01},

journal = {Synthetic Metals},

volume = {71},

number = {1-3},

pages = {1915-1916},

abstract = {The Cu NMR was performed to investigate an electronic property of a counterion site in (DMe-DCNQI)2Cu, (DMeO-DCNQI)2Cu, (DBr-DCNQI)2Cu, and partially deuterated (DMe-DCNQI-d2[1,1:0])2Cu. In these compounds, it is microscopically demonstrated that each metallic and insulating state possesses a similar electronic and magnetic properties and near the metal-insulator(M-I) boundary, any specific effect of electron correlation of d-electrons is not identified from a systematic measurements of the spin-lattice relaxation rate, (1/T1) of 63Cu. © 1995.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida1995881,

title = {1H NMR study in two dimensional Mott-Hubbard system, (BEDT-TTF)(TCNQ)},

author = {K Ishida and Y Niino and Y Kitaoka and K Asayama and Y Iwasa and Y Tokura},

doi = {10.1016/0379-6779(94)02689-V},

year  = {1995},

date = {1995-01-01},

journal = {Synthetic Metals},

volume = {70},

number = {1-3},

pages = {881-882},

abstract = {The 1H NMR measurement was carried out to investigate an electronic property of (BEDT-TTF)(TCNQ). There exist two magnetically different proton sites which belong to BEDT-TTF sheets and TCNQ columns. A distinct peak of 1/T1 appears at TN=3 K associated with the antiferromagnetic order, which coincides with the results suggested from the anisotropic susceptibility measurement. Any anomaly has not been identified at 35 K, below which a magnetic order was reported to occur in BEDT-TTF sheets. © 1995.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kitaoka199555,

title = {NMR study of strongly correlated electron systems},

author = {Y Kitaoka and H Tou and G -q Zheng and K Ishida and K Asayama and T C Kobayashi and A Kohda and N Takeshita and K Amaya and Y Onuki and G Geibel and C Schank and F Steglich},

doi = {10.1016/0921-4526(94)00365-3},

year  = {1995},

date = {1995-01-01},

journal = {Physica B: Physics of Condensed Matter},

volume = {206-207},

number = {C},

pages = {55-61},

abstract = {Various types of ground states in strongly correlated electron systems have been systematically investigated by means of NMR/NQR at low temperatures under high magnetic field and pressure. We focus on two well-known heavy-electron families, CeCu2X2 (X = Si and Ge) (Ce(122)) and UM2Al3 (M = Ni and Pd) (U(123)). The Cu NQR experiments on CeCu2X2 under high pressure indicate that the physical property of CeCu2Ge2 at high pressure, i.e. above the transition at 7.6 GPa from antiferromagnetic (AF) to superconductivity, are clearly related to tha CeCu2Si2 at ambient pressure. In addition to the H-T phase diagram established below 7 T, NMR and specific heat experiments on polycrystal CeCu2.05Si2 have revealed the presence of a new phase above 7 T. In a high-quality polycrystal of UPd2Al3 with a record high-Tc of 2 K at ambient pressure and the narrowest Al NQR line width, the nuclear-spin lattice relaxation rate, 27(1/T1) measured in zero field has been found to obey the T3 law down to 0.13 K, giving strong evidence that the energy gap vanishes along lines on the Fermi surface. Thus it seems that all heavy-electron superconductors exhibit lines of zero gap, regardless of their different magnetic properties. © 1995.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Zheng19952524,

title = {Local Hole Distribution in the CuO2 Plane of High-Tc Cu-Oxides Studied by Cu and Oxygen NQR/NMR},

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

doi = {10.1143/JPSJ.64.2524},

year  = {1995},

date = {1995-01-01},

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

volume = {64},

number = {7},

pages = {2524-2532},

abstract = {The hole numbers at Cu and oxygen sites in the CuO2 plane in a wide variety of high-Tc materials have been extracted from the measured nuclear quadrupole frequency, vQ. The hole number in the [formula omitted] orbit, [formula omitted] is found to be more than 0.85 in La2-xSrxCuO4 (x=0.075-0.24), while decreases to 0.74 in Tl2Ba2Ca2Cu3O10. Thus estimated [formula omitted] is supported by the result that the orbital Knight shift along the c-axis, [formula omitted] increases in proportion to [formula omitted] In contrast to the decrease of [formula omitted] the hole number in the O-2pσ orbit, [formula omitted] increases in going from the La- to the Tl-systems. It has been found that Tc is determined by two parameters about holes, i.e., [formula omitted] and [formula omitted] The former tells the microscopic “doping level” of the CuO2 plane, while a smaller [formula omitted] results in a weaker antifer-romagnetic spin fluctuations of low energy. It has been found that not only a proper [formula omitted] but also a sufficiently small [formula omitted] are needed to obtain a high value of Tc. © 1995, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida19952970,

title = {Cu NMR study in DCNQI-Cu system},

author = {K Ishida and Y Kitaoka and H Masuda and K Asayama and T Takahashi and A Kobayashi and R Kato and H Kobayashi},

doi = {10.1143/JPSJ.64.2970},

year  = {1995},

date = {1995-01-01},

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

volume = {64},

number = {8},

pages = {2970-2979},

abstract = {Cu-NMR measurement was made to investigate the electronic property of the counterion site in (DMe-DCNQI)2Cu and (DMeO-DCNQI)2Cu where the metallic state is stabilized down to low-T, (DBr-DCNQI)2Cu which exhibits the Metal-Insulator (MI) transition and partially deutrated (DMe-DCNQI-d2[1, 1; 0])2CU which experiences are-entrant (M-I-M) transition. In the metallic state, the nuclear-spin-lattice relaxation rate, 63(1/ T1) is found to follow nearly T 1T=const. law for all compounds except for (DMe-DCNQI)2Cu where (T1T)-1 is T-dependent above 100 K being scaled to the square of the d-spin part of the Knight shift, K3d(T) 2. From the analyses of 63(1/T1) , it is shown microscopically that the metallic state is usual, unaffected by the correlation effect among d-electrons. At the M-I transition, the value of 63(T1T)-1 and the Knight shift both being T-independent change discontinuously without any clear enhancement in the metallic region. The Cu-NMR results suggest that the d-electron correlation effect does not play a primary role for the M-I transition.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kitaoka19951931,

title = {NMR study in novel superconductors: Heavy-fermion system and high-Tc cuprate},

author = {Y Kitaoka and K Ishida and G -Q Zheng and H Tou and K Magishi and S Matsumoto and K Yamazoe and H Yamanaka and K Asayama},

doi = {10.1016/0022-3697(95)00098-4},

year  = {1995},

date = {1995-01-01},

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

volume = {56},

number = {12},

pages = {1931-1935},

abstract = {From the NMR and NQR studies, we show the unconventional superconducting properties in the antiferromagnetic (AF) heavy-fermion (HF), UPd2Al3 and high-Tc cuprate systems. In UPd2Al3 with TN = 14.5 K and Tc = 2 K, the superconductivity is shown to be of d-wave pairing type with lines of vanishing gap on the Fermi surface. The potential scattering associated with some defects at the Al site is the cause for the Tc suppression and the appearance of the density of states (DOS) at the Fermi level. This unusual impurity effect is consistent with a d-wave scenario, because the potential scattering leads to a gap opening for an anisotropic s-wave scenario. In high-Tc cuprate which are argued to be either a d-wave or an anisotropic s-wave, the potential scatterer like Zn in the plane induces the gapless superconductivity as well, which can not be interpreted in terms of an anisotropic s-wave scenario if the order parameter does not change sign largely. It is shown from the NMR experiment at the Al site for Al-doped La1.85Sr0.15CuO4 that local moments at near neighbor Cu sites induced around Al impurity do not play a role to suppress the Tc and to induce the DOS at all. The NMR studies in novel superconductors have provided important clues to identify their symmetry of order parameter to be d-wave. © 1995.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida19942113,

title = {63Cu and 17O NMR studies in the plane site in YBa2Cu3O7},

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

doi = {10.1016/0921-4526(94)91556-3},

year  = {1994},

date = {1994-01-01},

journal = {Physica B: Physics of Condensed Matter},

volume = {194-196},

number = {PART 2},

pages = {2113-2114},

abstract = {The temperature dependence of the nuclear-spin-lattice relaxation rate, 1/T1 of both Cu and O sites in the CuO2 plane have been measured at high magnetic field of 11T. The ratio of (1/T1(Cu)) / (1/T1(O)) (R) above Tc increases with decreasing temperature associated with the development of antiferromagnetic (AF) spin correlation and stays constantly below 100K, while R is rapidly reduced just below Tc, being different from the previous results. The decrease of R reflects intimately the reduction in the AF contribution to the spin-fluctuation spectral weight relative to the q∼ (0,0) part due to the gap opening. © 1994.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Azuma19941464,

title = {High Pressure Synthesis and Spin Gap of Quasi One Dimensional System Srn-1Cun+1O2n(n=3, 5)},

author = {M Azuma and Z Hiroi and M Takano and T Kitaoka and K Ishida},

doi = {10.2497/jjspm.41.1464},

year  = {1994},

date = {1994-01-01},

journal = {Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy},

volume = {41},

number = {12},

pages = {1464-1468},

abstract = {SrCu2O3 and Sr2Cu3O5 containing two-leg and three-legS= 1/2 ladders made of antiferromagnetic Cu-O-Cu linear bonds, respectively, were synthesized at high pressure, and their crystallographic and magnetic properties were investigated. Susceptibility of the 2-leg ladder system, SrCu2O3, showed a thermal excitation from the nonmagnetic ground state with a large spin gap of 420 K, while Sr2Cu3O5 containing 3-leg ladders had a finite susceptibility at the lowest temperature reflecting its gapless nature in the spin excitation spectrum. SrCu2O3 has thus been found to be the first 2-leg ladder compound having a well-defined spin gap. © 1994, Japan Society of Powder and Powder Metallurgy. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kitaoka19942052,

title = {Impurity Effect in High-Tc Superconductors —A Consistent Analysis by d-Wave Superconducting Model—},

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

doi = {10.1143/JPSJ.63.2052},

year  = {1994},

date = {1994-01-01},

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

volume = {63},

number = {6},

pages = {2052-2056},

abstract = {The contrast between Zn- and Ni-impurity effects in YBa2 Cu3 O7 and the imperfection-induced gapless superconductivity in Bi2Sr2CaCu2O8 reported previously are quantitatively analyzed based on the d-wave superconducting model. By taking account of the fact that the Zn impurity which caused the gapless superconductivity acts as a unitarity or strong scatterer, it is demonstrated that the Ni impurity does not give rise to the gapless superconductivity, although it is not so weak as to be treated in terms of Born scattering. The d-wave model can explain the characteristic feature such that even though Tc is moderately reduced by impurity scattering, the superconductivity changes into the gapless type with a finite density of states at the Fermi level. © 1994, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida1994563,

title = {63Cu nuclear relaxation study in the superconducting mixed state in YBa2Cu3O7. Magnetic excitation at low temperature},

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

doi = {10.1016/0038-1098(94)90121-X},

year  = {1994},

date = {1994-01-01},

journal = {Solid State Communications},

volume = {90},

number = {9},

pages = {563-566},

abstract = {63Cu spin-lattice relaxation rate 63(1/T1) at the CuO2 plane site in YBa2Cu3O7 has been measured under the strong magnetic field parallel and perpendicular to the c-axis in the oriented powder. The relaxation rate, 1/T1 in the mixed state at low temperatures, which has revealed almost a linear magnetic-field dependence, is dominated by the spin-diffusion process to the vortex cores. A most prominent finding is that the magnetic excitation in the normal vortex core is described in terms of T1T=const. law below about 10K. From the estimation of 1/T1 in the magnetic field induced normal state in YBa2Cu3O7, it is demonstrated that the normal state could be treated within the framework of the Fermi liquid picture at low temperatures, if the superconductivity were destroyed by the magnetic field. © 1994.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ohsugi19942057,

title = {Observation of Magnetic Ordering in La2-xSrxCuO4 around x=0.115-La-NQR Study-},

author = {S Ohsugi and H Yamanaka and K Ishida and K Asayama},

doi = {10.1143/JPSJ.63.2057},

year  = {1994},

date = {1994-01-01},

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

volume = {63},

number = {6},

pages = {2057-2060},

abstract = {The nuclear quadrupole resonance (NQR) study of 139La in La2_xSrxCuO4 was systematically carried out in the Sr-content range from 0.085 to 0.15 at 1.4 and 4.2 K in zero field. The linewidth of the I39La NQR spectrum for the (± 1/2→±3/2) transition was found to increase especially at x=0.115, associated with the occurrence of magnetic ordering. This is hence considered to be responsible for the decrease of the superconducting transition temperature around x=0.115. Since the spectrum does not broaden with for the (±5/2→±7/2) transition down to 1.4 K, the ordered Cu-moments are considered to exist in the Cu-O2 sheets. © 1994, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida19941629,

title = {63Cu NMR study in non-doped and Y-doped Bi2Sr2CaCu2O8 single crystals},

author = {K Ishida and Y Kitaoka and K Asayama and K Kadowaki and T Mochiku},

doi = {10.1016/0921-4534(94)92040-0},

year  = {1994},

date = {1994-01-01},

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

volume = {235-240},

number = {PART 3},

pages = {1629-1630},

abstract = {The normal and superconducting properties in single crystals Bi2Sr2CaCu2O8 (Bi2212) and Bi2Sr2(Ca0.95Y0.05)Cu2O8 (5%Y-doped Bi2212) have been investigated by systematic measurements of the 63Cu Knight shift, 63K(T) and the nuclear spin-lattice relaxation time, 63T1. © 1994.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Azuma19943463,

title = {Observation of a spin gap in SrCu2O3 comprising spin- Quasi-1D two-leg ladders},

author = {M Azuma and Z Hiroi and M Takano and K Ishida and Y Kitaoka},

doi = {10.1103/PhysRevLett.73.3463},

year  = {1994},

date = {1994-01-01},

journal = {Physical Review Letters},

volume = {73},

number = {25},

pages = {3463-3466},

abstract = {Magnetic properties of SrCu2O3 and Sr2Cu3O5, containing two-leg and three-leg S=12 ladders made of antiferromagnetic Cu-O-Cu linear bonds, were investigated. The susceptibility of the two-leg ladder material, SrCu2O3, is characteristic of thermal excitation from a nonmagnetic ground state with a spin gap of about 420 K, while the susceptibility of Sr2Cu3O5, containing three-leg ladders, reflects a gapless spin excitation spectrum. The temperature dependence of the nuclear-spin lattice relaxation rate, 1T1, of Cu63 NMR also indicates the existence of a spin gap only for SrCu2O3. The spin gap we observed for SrCu2O3 confirms a recent theoretical prediction for the magnetic behavior of spin = antiferromagnetically coupled Heisenberg chains. © 1994 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ishida19941104,

title = {Cu NMR Study in Single Crystal Bi2 Sr2 CaCu2 O8 -Observation of Gapless Superconductivity-},

author = {K Ishida and Y Kitaoka and K Asayama and K Kadowaki and T Mochiku},

doi = {10.1143/JPSJ.63.1104},

year  = {1994},

date = {1994-01-01},

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

volume = {63},

number = {3},

pages = {1104-1113},

abstract = {The normal and superconducting properties in single crystal Bi2Sr2CaCu2O8 (Bi2212) with TC=86K have been investigated by systematic measurements of the 63Cu Knight shift, 63K(T) and the nuclear-spin-lattice relaxation time, T1. In the normal state, the T-dependences of 63K(T) and (T1 T)-1 in Bi2212 share similar magnetic behaviors to the underdoped systems such as oxygen deficient YBa2Cu3 06+x and YBa2Cu4O8, namely, 63K(T) decreases with lowering temperature and 63(T1 T)-1 has a peak above Tc. However, from the analyses of the anisotropy of 1/T1 and the hypernne field, Bi2212 is found to belong to the slightly over-doped region as in Tl2Ba2Cu06+x and TlSr2CaCu2O8-x. In the superconducting state, the finding of T1 T= const, law far below Tc has revealed that the superconductivity is in a gapless regime, accompanied by the finite density of states at the Fermi level. © 1994, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ohsugi1994700,

title = {Cu NMR and NQR Studies of High-Tc Superconductor La2-xSrxCuO4},

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

doi = {10.1143/JPSJ.63.700},

year  = {1994},

date = {1994-01-01},

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

volume = {63},

number = {2},

pages = {700-715},

abstract = {Result of extensive Cu NMR and NQR studies in the superconducting La2-x Srx,CuO4 with x=0.075∼0.24 have been presented. The rapid decrease of the nuclear spin-lattice relaxation rate, 1/T1, and the spin Knight shift below Tc confirm microscopically the existence of the superconducting phase with lower Tc than 38 K for 0.10≤x0.24. For x=0.10, magnetic anomalies emerge at low-T in some small parts of the sample, e.g. T-independent T1 and broadening of spectrum, having some relevance to the magnetic order in La2-xBaxCuO4 with x=0.125. For x>0.15 the T1, T-const, behavior and the existence of the residual spin Knight shift far below Tc have revealed that the superconductivity is of a gapless type with a finite density of states at the Fermi level caused by the mixture of different structures, i.e. tetragonal and orthorhombic. La2-xSrxCuO4, high-Tc superconductivity, Cu nmr and nqr, d-wave gapless superconductivity, antiferromagnetic spin correlation, structural instability. © 1994, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}