論文リスト

@article{Bao1996256,

title = {Relation between transport, structural and superconductive properties in La2-x-yNdyBaxCuO4},

author = {X Z Bao and J Nyhus and Y Maeno and Y Tanaka and S Sakita and T Fujita},

doi = {10.1016/S0921-4534(96)00540-0},

year  = {1996},

date = {1996-01-01},

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

volume = {271},

number = {3-4},

pages = {256-264},

abstract = {The interplay between transport properties, structural phase transitions and superconductivity in La2-x-yNdyBaxCuO4 (y = 0.20) has been studied. We found that the temperature at which the thermopower S(T) begins to show an unusual decrease on cooling coincides with that of the minimum in the resistivity for the samples with x around 1/8. Moreover, the appearance of negative thermopower accompanies the suppression of superconductivity. In contrast, we did not find any anomaly in the thermopower at the structural phase transition temperature Td2 for any of the samples in this study. The results show that in this series of compounds, the suppression of superconductivity around x = 1/8 is not directly associated with the structural phase transition but with the profound change of the transport properties. The present results are consistent with the charge ordering as suggested by recent electron diffraction as well as neutron diffraction studies.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Inoue1996516,

title = {Redistribution of the spectral intensity in a layered 4d-electron superconductor Sr2RuO4 observed by the photoemission spectroscopy},

author = {I H Inoue and Y Aiura and Y Nishihara and Y Haruyama and S Nishizaki and Y Maeno and T Fujita and J G Bednorz and F Lichtenberg},

doi = {10.1016/0921-4526(96)00160-3},

year  = {1996},

date = {1996-01-01},

journal = {Physica B: Condensed Matter},

volume = {223-224},

number = {1-4},

pages = {516-518},

abstract = {Spectra from photoemission spectroscopy (PES) of a recently discovered layered-perovskite superconductor Sr2RuO4 are reported. The PES spectrum of Sr2RuO4 around the Fermi level (EF) is apparently different from the non-interacting density of states obtained by a band calculation, suggesting the importance of strong electron correlation in this system.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Mackenzie19963786,

title = {Quantum oscillations in the layered perovskite superconductor Sr2RuO4},

author = {A P Mackenzie and S R Julian and A J Diver and G J McMullan and M P Ray and G G Lonzarich and Y Maeno and S Nishizaki and T Fujita},

doi = {10.1103/PhysRevLett.76.3786},

year  = {1996},

date = {1996-01-01},

journal = {Physical Review Letters},

volume = {76},

number = {20},

pages = {3786-3789},

abstract = {We report a comprehensive study of magneto-oscillatory phenomena in the normal state of Sr2RuO4, the first layered perovskite superconductor (TC ≅ 1K) not based on copper. The form of the quasiparticle spectrum observed may be interpreted in terms of an almost two-dimensional Fermi liquid model which is consistent with Luttinger's theorem and successfully predicts bulk thermodynamic and transport properties at low temperatures. A study of the spectra and transport along the c axis provides insights into the different normal state and superconducting behavior of Sr2RuO4 and the cuprates. © 1996 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Sakita1996216,

title = {Elastic softening in single-crystalline La2 - XSrxCuO4 around x = 1/8},

author = {S Sakita and T Suzuki and F Nakamura and M Nohara and Y Maeno and T Fujita},

doi = {10.1016/0921-4526(95)00700-8},

year  = {1996},

date = {1996-01-01},

journal = {Physica B: Condensed Matter},

volume = {219-220},

number = {1-4},

pages = {216-218},

abstract = {Ultrasound measurements have revealed a remarkable lattice softening of the transverse elastic modulus (C11 - C12)/2 in single-crystalline La2 - xSrxCuO4 only around x = 1/8. Analysis of the temperature dependence of the elastic modulus indicates that in the particular range of carrier concentration there exists a narrow electronic band in the vicinity of the Fermi level which couples to the shearing strain εxx - εyy.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Udagawa1996222,

title = {Phonon Raman scattering of Sr2RuO4},

author = {M Udagawa and T Minami and N Ogita and Y Maeno and F Nakamura and T Fujita and J G Bednorz and F Lichtenberg},

doi = {10.1016/0921-4526(95)00702-4},

year  = {1996},

date = {1996-01-01},

journal = {Physica B: Condensed Matter},

volume = {219-220},

number = {1-4},

pages = {222-224},

abstract = {Phonon Raman scattering spectra of Sr2RuO4 have been measured in the temperature region between room temperature and 5 K. Three symmetry-allowed phonons have been observed at room temperature. Since similar spectra have been observed at low temperature, Sr2RuO4 does not undergo structural phase transitions in the temperature region. The energy of the phonon modes has been calculated by a GF matrix method. The force constants along the c-axis of Sr2RuO4 are larger than those for La2 - xSrxCuO4.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nishizaki19961876,

title = {Effect of Annealing on the Superconductivity of Sr2RuO4},

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

doi = {10.1143/JPSJ.65.1876},

year  = {1996},

date = {1996-01-01},

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

volume = {65},

number = {6},

pages = {1876-1877},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Yoshida19962220,

title = {Anisotropic Flux Pinning in a Layered Superconductor Sr2RuO4},

author = {K Yoshida and Y Maeno and S Nishizaki and T Fujita},

doi = {10.1143/JPSJ.65.2220},

year  = {1996},

date = {1996-01-01},

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

volume = {65},

number = {7},

pages = {2220-2226},

abstract = {We found peculiar flux-pinning in single crystals of Sr2RO4, the only known layered-perovskite superconductor without copper. Measurements on ac susceptibility under dc magnetic fields indicate that a second dissipation peak prominently appears only when the direction of the flux lines, as well as of their induced motions, is parallel to the ab planes. The anisotropic nature of this peak effect is clearly different from that reported in high-Tc cuprates, the other class of layered perovskite superconductors. The peak effect in Sr2RuO2 is attributed to the synchronization of the flux lines to the pinning centers as the flux-line lattice softens with increasing magnetic field and temperature.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nohara1995570,

title = {Unconventional lattice stiffening in superconducting La2-xSrxCuO4 single crystals},

author = {M Nohara and T Suzuki and Y Maeno and T Fujita and I Tanaka and H Kojima},

doi = {10.1103/PhysRevB.52.570},

year  = {1995},

date = {1995-01-01},

journal = {Physical Review B},

volume = {52},

number = {1},

pages = {570-580},

abstract = {Ultrasonic and specific-heat measurements have been performed on single crystals of La2-xSrxCuO4 (LSCO) with x=0.09, 0.14, and 0.19 across the superconducting transition temperature Tc. We observed jumplike decreases in the longitudinal elastic moduli at Tc, as are seen in conventional superconductors. Anisotropic strain dependence of Tc was estimated from both the jump in the elastic moduli and specific heat at Tc via the Ehrenfest relation. With further lowering temperature below Tc, we found a pronounced lattice stiffening in the elastic moduli of LSCO, which contrasts with the continuous softening observed in most of the conventional superconductors. Thermodynamic analysis revealed that the stiffening originates from the change in the superconducting condensation energy under the lattice strain. This unusual lattice stiffening in the superconducting state is possibly a common character of the high-Tc copper oxides. © 1995 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Shirakawa19951072,

title = {Novel Hall-Coefficient Behavior in Superconducting Sr2RuO4},

author = {N Shirakawa and K Murata and Y Nishihara and S Nishizaki and Y Maeno and T Fujita and J G Bednorz and F Lichtenberg and F Lichtenberg and N Hamada},

doi = {10.1143/JPSJ.64.1072},

year  = {1995},

date = {1995-01-01},

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

volume = {64},

number = {4},

pages = {1072-1075},

abstract = {We present the temperature dependence of the Hall coefficient (RH) of Sr2RuO4, in which superconductivity with Tc = 0.93 K has been discovered recently. The value of RH shows strong temperature dependence, and sign reversal occurs at around 20 K, i.e., RH is positive and small (≤2 × 10−11 m3 C−1) for T>20 K, while for T<20 K RHis negative and |RH| continuously increases at least down to 1.8 K, where RH=−1.37 × 10−10 m3 C−1. A possible mechanism of the temperature dependence of RH, involving the electron-correlation effect, is discussed. © 1995, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.},

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{Yoshida1994371,

title = {Ion-size effects on the structure and superconductivity of La-214 compounds at 1 8 doping},

author = {K Yoshida and F Nakamura and Y Tanaka and Y Maeno and T Fujita},

doi = {10.1016/0921-4534(94)90853-2},

year  = {1994},

date = {1994-01-01},

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

volume = {230},

number = {3-4},

pages = {371-377},

abstract = {A structural transition to a low-temperature tetragonal (TLT) phase occurs below Td2≈60 K in La2-xBaxCuO4 only around x=0.125, accompanied by sharp suppression of superconductivity. In this study we investigated the effects of partial substitution of smaller divalent cations for Ba2+ ions (Ba2+ > Sr2+ > Ca2+) on these anomalous low-temperature properties. The suppression of superconductivity is strongly affected by the appearance of the TLT phase for this carrier concentration. We also show that the variations of Td2 and Tc are quantitatively scaled by the averaged size of cations at the La site. This dependence can be interpreted as chemical effects acting effectively as applied pressure. We discuss how our observation is related to recent reports which claim that the TLT structure itself does not necessarily destroy the superconductivity. © 1994.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Suzuki1994419,

title = {Lattice instability in the normal state of La2-xSrxCuO4},

author = {T Suzuki and M Nohara and Y Maeno and T Fujita and I Tanaka and H Kojima},

doi = {10.1007/BF00724580},

year  = {1994},

date = {1994-01-01},

journal = {Journal of Superconductivity},

volume = {7},

number = {2},

pages = {419-421},

abstract = {Novel softening has been found in the transverse elastic constant (C11-C12)/2 below 50 K in single-crystalline La1.86Sr0.14CuO4 (LSCO) by high-precision ultrasonic measurements in magnetic fields H along the c axis. With decreasing temperature, this lattice softening persists down to the superconducting transition temperature Tc(H), which is reduced to 14 K by applying fields up to 14 T. Below Tc(H) the softening turns to rapid hardening. This behavior indicates the presence of lattice instability of the orthorhombic (Bmab) structure in the normal state of LSCO, which disappears in the superconducting state. This is evidence for the intimate interplay between high-Tc superconductivity and the lattice instability in LSCO. © 1994 Plenum Publishing Corporation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Tanaka19942053,

title = {Structural transitions in La2-y-xNdyBaxCuO4 with x=0.125},

author = {Y Tanaka and Y Maeno and F Nakamura and T Fujita},

doi = {10.1016/0921-4526(94)91526-1},

year  = {1994},

date = {1994-01-01},

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

volume = {194-196},

number = {PART 2},

pages = {2053-2054},

abstract = {The structural transition to a low-temperature tetragonal phase in La2-xBaxCuO4 occurs at the hole concentration p∼ 1 8. We have studied the structural and electrical properties of La2-y-xNdyBaxCuO4 with x=0.125 to clarify the effect of substitution by trivalent ions. The substitution by Nd3+ enhances the structural transition temperature without changing of p. This enhancement is qualitatively explained by the crystallochemical origin. © 1994.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Yoshida19942051,

title = {Effects of ionic size on the x= 1 8 anomaly in La2-xBax-yMyCuO4 (M=Ca,Sr)},

author = {K Yoshida and F Nakamura and Y Tanaka and Y Maeno and T Kagayama and G Oomi and T Fujita},

doi = {10.1016/0921-4526(94)91525-3},

year  = {1994},

date = {1994-01-01},

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

volume = {194-196},

number = {PART 2},

pages = {2051-2052},

abstract = {A structural transition at about 60 K occurs in La2-xBaxCuO4 only around x = 1 8, accompanied by suppression of superconducting transition temperature Tc. Partial substitution of smaller divalent ions for Ba2+ ions (Ba2+ > Sr2+ > Ca2+) leads to suppression of this low-temperature structural transition. The structural transition temperature is scaled quantitatively with the average size of divalent ions. Furthermore, this dependence corresponds well to chemical pressure effects. © 1994.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nohara19942167,

title = {Effects of superconductivity on elastic constants of La2-xSrxCuO4},

author = {M Nohara and S Nishigori and T Suzuki and Y Maeno and T Fujita and I Tanaka and H Kojima},

doi = {10.1016/0921-4526(94)91583-0},

year  = {1994},

date = {1994-01-01},

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

volume = {194-196},

number = {PART 2},

pages = {2167-2168},

abstract = {Ultrasonic and specific-heat measurements have been performed across the superconducting transition on a single crystal of La1.86Sr0.14CuO4. A pronounced jump of the elastic constant ΔC33(Tc) = -0.15 GPa is observed at Tc = 34 K as well as a specific-heat jump Δcp/Tc = 9.6 mJ/K2mol, whereas a jump in C11 is less obvious. The results allow quantitative estimation of the strain dependence of Tc and the condensation energy along the a and c axes. © 1994.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Maeno199439,

title = {Structural instabilities and superconductivity in La-214 compounds},

author = {Y Maeno and M Nohara and F Nakamura and T Suzuki and T Fujita},

doi = {10.1007/BF00730365},

year  = {1994},

date = {1994-01-01},

journal = {Journal of Superconductivity},

volume = {7},

number = {1},

pages = {39-43},

abstract = {In La2-xBaxCuO4 (LBCO) the transition to a low-temperature tetragonal phase and the suppression of superconductivity occur at the carrier concentration p≈ 1/8 per copper. We will discuss the roles of various material parameters that control this instability. An unusual lattice softening has been found by ultrasonic measurement on La2-xSrxCuO4 (LSCO). This softening is present only in an in-plane shearing mode and is ascribed to the growth of structural fluctuations in the normal state. These phenomena are closely related because both the structural change in LBCO and the applied strain in LSCO lift the degeneracy of in-plane oxygen sites. They clarify the importance of strong coupling between the normal-state electronic system and the lattice by a Peierls-type mechanism. © 1994 Plenum Publishing Corporation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nakamura199433,

title = {Stability of the low-temperature tetragonal phase in La2-xBaxCuO4 and related compounds},

author = {F Nakamura and K Yoshida and Y Tanaka and X Z Bao and Y Maeno and T Fujita},

doi = {10.1007/BF00730363},

year  = {1994},

date = {1994-01-01},

journal = {Journal of Superconductivity},

volume = {7},

number = {1},

pages = {33-35},

abstract = {In La2-xBaxCuO4 (LBCO), the structural transition to a low-temperature tetragonal phase below 60 K and suppression of superconductivity are observed when the carrier density is p ∼ 1 /8 per copper. The replacement by divalent ions smaller than Ba2+ suppresses the static deformation of the lattice. We have found that the variations Td2 and superconducting transition temperature Tc are quantitatively characterized by the averaged ionic radius at the La site or lattice parameters. This aspect of substitution could be regarded as the effect of chemical pressure, since similar variations have been reported on applying hydrostatic pressure. In La2-x-yNdy(Ba, Sr)xCuO4, Td2 increases with increasing y in a wide range of p while Tc is suppressed only at p∼ l /8. The structural transition at Td2 here should be ascribed mainly to the crystallochemical origin. © 1994 Plenum Publishing Corporation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nakayama19941283,

title = {Anisotropy in thermal expansion of La2-xSrxCuO4},

author = {S Nakayama and Y Maeno and M Irie and M Nohara and F Nakamura and T Fujita},

doi = {10.1016/0921-4534(94)91866-X},

year  = {1994},

date = {1994-01-01},

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

volume = {235-240},

number = {PART 2},

pages = {1283-1284},

abstract = {We report on the anisotropy of thermal expansion α of La2-xSrxCuO4 (x=0.14) detwinned single crystals. Using observed discontinuities in α at the tetragonal-orthorhombic transition temperature, Td, the uniaxial stress dependence along the a-, b- and c-axis are estimated as dTddPi=a,b,c,∼+130, -310 and +60 K/GPa, respectively. We also discuss the structural fluctuation near Td. © 1994.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nohara19941249,

title = {Unconventional enhancement of elastic constants in superconducting La2-xSrxCuO4},

author = {M Nohara and T Suzuki and Y Maeno and T Fujita and I Tanaka and H Kojima},

doi = {10.1016/0921-4534(94)91849-X},

year  = {1994},

date = {1994-01-01},

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

volume = {235-240},

number = {PART 2},

pages = {1249-1250},

abstract = {Ultrasonic measurements were performed on single crystals of La2-xSrxCuO4 (LSCO) with x = 0.09, 0.14 and 0.19. We found that the elastic constants of LSCO increase well below the superconducting transition temperature Tc, in contrast with softeniing observed in conventional superconductors. The difference originates from the change in superconducting condensation energy ø under the lattice strain εi induced by a sound wave. © 1994.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nakamura19941285,

title = {Structural and transport properties of detwinned crystals of La2-xSrxCuO4},

author = {F Nakamura and M Kodama and S Nishizaki and Y Tanaka and Y Maeno and T Fujita},

doi = {10.1016/0921-4534(94)91867-8},

year  = {1994},

date = {1994-01-01},

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

volume = {235-240},

number = {PART 2},

pages = {1285-1286},

abstract = {We studied a process of detwinning of La2-xSr2CuO4 (x=0.14) by X-ray diffraction measurements between 5 and 300K. Detwinned crystals are obtained by cooling under a small uniaxial pressure of about 2MPa along the tetragonal 〈110〉T direction. We also report on the effect of twin formation on the inplane transport properties. © 1994.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Maeno1994532,

title = {Superconductivity in a layered perovskite without copper},

author = {Y Maeno and H Hashimoto and K Yoshida and S Nishizaki and T Fujita and J G Bednorz and F Lichtenberg},

doi = {10.1038/372532a0},

year  = {1994},

date = {1994-01-01},

journal = {Nature},

volume = {372},

number = {6506},

pages = {532-534},

abstract = {FOLLOWING the discovery of superconductivity at ∼30 K in La2-xBaxCuO4 (ref. 1), a large number of related compounds have been found that are superconducting at relatively high temperatures. The feature common to all of these materials is a layered crystal structure based on a perovskite template and containing planar networks of copper and oxygen. This raises the question of whether superconductivity can occur in layered perovskites that do not contain copper. To the best of our knowledge, no such material has been found to date, despite nearly a decade of searching. We describe here the discovery of superconductivity in Sr2RuO4, a layered perovskite isostructural with La2-xBaxCuO4 (Fig. 1). Our results demonstrate that the presence of copper is not a prerequisite for the existence of superconductivity in a layered perovskite. But the low value of the superconducting transition temperature (Tc Combining double low line 0.93 K) points towards a special role for copper in the high-temperature superconductors.},

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}

}

@article{Nohara19933447,

title = {Interplay between lattice softening and high-Tc superconductivity in La1.86Sr0.14CuO4},

author = {M Nohara and T Suzuki and Y Maeno and T Fujita and I Tanaka and H Kojima},

doi = {10.1103/PhysRevLett.70.3447},

year  = {1993},

date = {1993-01-01},

journal = {Physical Review Letters},

volume = {70},

number = {22},

pages = {3447-3450},

abstract = {High-resolution ultrasonic measurements have been performed on single-crystalline La1.86Sr0.14CuO4 in magnetic fields H up to 14 T. We found that by reducing temperature the transverse elastic constant (C11-C12)/2 starts to soften from about 50 K and continues to soften down to Tc(H), even when Tc(H) is reduced to 14 K by magnetic field. The softening turns to rapid hardening by the emergence of superconductivity. This behavior of C(11-C12)/2 is a consequence of the structural instability of the orthorhombic phase and disappearance of the instability caused by emergence of the superconducting state. © 1993 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Udagawa199311391,

title = {Phonon Raman scattering of (La1-xSrx)2NiO4},

author = {M Udagawa and T Yamaguchi and Y Nagaoka and N Ogita and M Kato and Y Maeno and T Fujita and K Ohbayashi},

doi = {10.1103/PhysRevB.47.11391},

year  = {1993},

date = {1993-01-01},

journal = {Physical Review B},

volume = {47},

number = {17},

pages = {11391-11397},

abstract = {Phonon Raman spectra of polycrystalline (La1-xSrx)2NiO4 have been investigated at 500, 300, 77, and 10 K in the Sr-concentration region less than 0.6. We have observed two peaks at about 220 cm-1 (R1) and at about 460 cm-1 (R2). They are assigned to an apical-oxygen motion along the a axis with Eg symmetry and an apical-oxygen motion along the c axis with A1g symmetry, respectively. With increasing x at room temperature, the energy of R1 is constant for 0<x≤0.3, decreases by about 10 cm-1 for 0.3<x<0.4, and is constant for x0.4, while that of R2 is almost constant for x≤0.3 and increases for x>0.3. Similar concentration dependences have been observed at 500, 77, and 10 K. To clarify the concentration dependence of the observed phonon energies, we have calculated the energies of normal modes at a k=0 point by the GF-matrix method. In the calculation, six kinds of longitudinal force constants have been taken. The best fitting has been made for the data at room temperature. The concentration dependence of the observed Raman modes can be mainly explained by the change of the corresponding force constants; for R1 a force constant due to the La-O bond in the La-O layers and for R2 the sum of force constants due to the Ni-O and La-O bonds along the c axis, respectively. As a comparison, we have measured Raman spectra of (La1-xSrx)2CuO4 (x≤0.2). We have found that the mode at about 230 cm-1, which corresponds to the R1 mode in La2NiO4, decreases by 6 cm-1 for x=0.2. It can be concluded that the doping of divalent ions decreases the bond stiffness in the La-O block layers for the La-based copper oxide superconductor. © 1993 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lang1992482,

title = {Lattice instabilities in cuprate superconductors: A possible limiting mechanism for Tc},

author = {M Lang and R K̈rsch and A Grauel and C Geibel and F Steglich and H Rietschel and T Wolf and Y Hidaka and K Kumagai and Y Maeno and T Fujita},

doi = {10.1103/PhysRevLett.69.482},

year  = {1992},

date = {1992-01-01},

journal = {Physical Review Letters},

volume = {69},

number = {3},

pages = {482-485},

abstract = {High-resolution thermal-expansion experiments on (i) insulating La2CuO4+, (ii) its Sr- and Ba-doped metallic counterparts with reduced Tc values, and (iii) Nd1.85Ce0.15CuO4- (Tc24 K) reveal distinct lattice instabilities at T1=321 K and T2=361 K. T2 coincides with Tcmax found upon 15 at.% Sr doping. For YBa2Cu3O6.5 (Tc=49 K), a lattice instability occurs at T=901 K, i.e., again close to Tcmax=92 K. © 1992 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Maeno1991909,

title = {Effects of Th-doping on the anomalous low-temperature properties of La2-xBaxCuO4},

author = {Y Maeno and N Kakehi and M Kato and Y Tanaka and T Fujita},

doi = {10.1016/0921-4534(91)91678-W},

year  = {1991},

date = {1991-01-01},

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

volume = {185-189},

number = {PART 2},

pages = {909-910},

abstract = {Study of low-temperature lattice instabilities and superconductivity in Th-doped La2-xBaxCuO4, La2-y-xThyBaxCuO4, revealed that a low-temperature tetragonal (TLT) phase and sharp suppression of Tc are most prominent at x - y ≊ 0.125, instead of x ≊ 0.125. Thefore, the anomalous low-temperature behavior is essentially controlled by the carrier concentration, rather than local ionic forces. © 1991.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nakamura19911103,

title = {Magnetic and transport properties of La2-xSrxCuOy near x = 1},

author = {F Nakamura and K Yoshida and K Sugiyama and Y Maeno and T Fujita},

doi = {10.1016/0921-4534(91)91775-Y},

year  = {1991},

date = {1991-01-01},

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

volume = {185-189},

number = {PART 2},

pages = {1103-1104},

abstract = {The dependence of magnetic and electric properties of Sr content is studied for heavily Sr-doped La2-xSrxCuOy with 0.4 ≤ x ≤ 1.0. Curie-Weiss susceptibility and electron-spin resonance (ESR) spectra for Cu2+ ions are observed for samples near x = 1. We discuss the antiferromagnetic coupling for x = 1.0 in comparson with that for x = 0. © 1991.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Ekino1991845,

title = {Feasibility of electron donation to the CuO2 plane of mono-layer copper oxides by hydrogen absorption},

author = {T Ekino and K Matsukuma and T Takabatake and Y Maeno and H Fujii},

doi = {10.1016/0921-4534(91)91646-L},

year  = {1991},

date = {1991-01-01},

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

volume = {185-189},

number = {PART 2},

pages = {845-846},

abstract = {The hydrogenation effect on the hole-doped La2-xSrxCuO4-z and electron-doped Nd2-xCexCuO4-z have been investigated. Systematic shift of the phase diagram of La2-xSrxCuO4-z by hydrogenation indicates that the absorbed hydrogen plays a role of electron donor to the CuO2 plane. On the other hand, in Nd2-xCexCuO4-zHy, the sharp boundary between the normal and superconducting phases at x=0.14 was found to be independent of y, indicating that the absorbed hydrogen can not donate electrons to the CuO2 plane, unlike the hole-doped copper oxide superconductors. © 1991.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Nohara19911397,

title = {Anisotropic coupling between high-Tc superconductivity and lattice in single-crystalline La1.86Sr0.14CuO4},

author = {M Nohara and T Suzuki and Y Maeno and T Fujita and I Tanaka and H Kojima},

doi = {10.1016/0921-4534(91)91922-Q},

year  = {1991},

date = {1991-01-01},

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

volume = {185-189},

number = {PART 2},

pages = {1397-1398},

abstract = {The longitudinal elastic constants in high-quality single crystals La1.86Sr0.14CuO4 were measured across the superconducting transition temperature Tc under magnetic fields up to 14T applied both parallel and normal to the CuO2-plane. We found anomalies of elastic constants at Tc, indicating the anisotropic coupling between the high- Tc superconductivity and lattice. We newly found anomalies below 4K under high field, suggesting the field induced instability of the lattice. © 1991.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Maeno1991587,

title = {Simple and reliable method for determination of oxygen content in high-Tc copper oxides},

author = {Y Maeno and H Teraoka and K Matsukuma and K Yoshida and K Sugiyama and F Nakamura and T Fujita},

doi = {10.1016/0921-4534(91)92096-T},

year  = {1991},

date = {1991-01-01},

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

volume = {185-189},

number = {PART 1},

pages = {587-588},

abstract = {We present the details of a simple and reliable iodine-titration method suited for high-Tc copper oxides, in which the use of a solution of ammonium acetate and acetic acid as a buffer agent substantially improves the operation. The results applied to La2-xMxCuO4-δ (M = Ba, Sr and Ca) are presented. © 1991.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Lang19911347,

title = {Thermal expansion derived lattice instabilities near maximum Tc in high-Tc cuprates},

author = {M Lang and R Kürsch and F Steglich and T Wolf and Y Maeno and K Kumagai and Y Hidaka},

doi = {10.1016/0921-4534(91)91897-D},

year  = {1991},

date = {1991-01-01},

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

volume = {185-189},

number = {PART 2},

pages = {1347-1348},

abstract = {For the "214" cuprates, La2CuO4+δ, La2-xMxCuO4 (M = Sr,Ba) and Nd1.85Ce0.15CuO3.998, thermal expansion measurements reveal lattice instabilities at T1 = 31K and T2 = 36K. T2 coincides with Tcmax found upon 15 at% Sr doping. For YBa2Cu3O6.5 (Tc = 49K) a lattice instability occurs at T = 90K, again close to Tcmax. © 1991.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Udagawa19911039,

title = {Raman scattering study of (La1-xSrx)2NiO4},

author = {M Udagawa and T Yamaguchi and N Ogita and K Ohbayashi and M Kato and Y Maeno and T Fujita},

doi = {10.1016/0921-4534(91)91743-N},

year  = {1991},

date = {1991-01-01},

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

volume = {185-189},

number = {PART 2},

pages = {1039-1040},

abstract = {Phonon Raman spectra of polycrystalline (La1-xSrx)2NiO4 crystals have been measured at room temperature and at liquid nitrogen temperature for x=0, 0.1, 0.2, 0.25, 0.3, 0.35, 0.4, 0.5. We have observed two Raman active phonons at about 450cm-1 and at about 240cm-1. We assign the mode at 450cm-1 to NiO stretching along c-axis (Alg) and that at 240cm-1 to optical oxygen along a- or b-axis (Eg). The frequencies of the Alg mode does not show a distinct Sr dependence. While the energy of the Eg mode strongly depends on x; with increasing x, the energy of the Eg mode decreases for x<0.3 and slightly increases for x>0.3. We have found that the x value of the minimum energy corresponds to the characteristic concentration, where the electronic conduction changes from semiconductive to metallic. We suggest that the Eg mode couples with the electronic state of (Lal-xSrx)2NiO4. © 1991.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Keller19911089,

title = {Muon-spin rotation (μSR) study of the temperature dependence of the London penetration depth in copper oxide superconductors},

author = {H Keller and W Kündig and I M Savić and H Simmler and B Stäuble-pümpin and M Warden and D Zech and P Zimmermann and E Kaldis and J Karpinski and S Rusiecki and J H Brewer and T M Riseman and J W Schneider and Y Maeno and C Rossel},

doi = {10.1016/0921-4534(91)91768-Y},

year  = {1991},

date = {1991-01-01},

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

volume = {185-189},

number = {PART 2},

pages = {1089-1090},

abstract = {A μSR study of the temperature dependence of the London penetration depth λ in sintered samples of YBa2Cu3Oz (with various oxygen contents x), YBa2Cu4O8 and Bi2Sr2CaCu2O8 is presented. It is found that the temperature behavior of λ of all these cuprate superconductors is consistent with conventional s-wave pairing. However, there are significant differences concerning the exact temperature dependence of λ in these materials. In YBa2Cu3Oz with high x, the behavior of λ(T) is well described by the two-fluid model (strong coupling), whereas λ(T) in YBa2Cu3Oz with low x, YBa2Cu4O8 and Bi2Sr2CaCu2O8 is in better agreement with weak-coupling BCS theory. Possible reasons for the different temperature behavior of λ in these materials are discussed. © 1991.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kato1991533,

title = {Two-dimensional antiferromagnetic correlation with spin 1 2 in magnetic susceptibility of (La, Sr)2NiO4},

author = {M Kato and Y Maeno and T Fujita},

doi = {10.1016/0921-4534(91)90060-C},

year  = {1991},

date = {1991-01-01},

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

volume = {176},

number = {4-6},

pages = {533-540},

abstract = {Measurements of the magnetic susceptibility χ of nonsuperconducting (La1-χSrχ)2NiO4 (LSNO) with χ close to 0.5 between 5 and 700 K revealed the presence of a broad peak in the temperature dependence of χ as observed in superconducting (La1-χSrχ)2CuO4 (LSCO). The broad peak is attributed to the two-dimensional antiferromagnetic (2DAF) correlation between S = 1 2 spins of Ni3+ in the low-spin state. However, contrary to LSCO, the peak temperature, Tmax, which is related to the correlation energy J, increases with χ for LSNO. In LSNO eg electrons are distributed to the 3dx2-y2 and 3dz2 orbitals, both of which are not completely occupied. A strong 2DAF correlation exists among Ni3+ spins in a (3dx2-y2)1 configuration. With increasing χ, the fraction of Ni3+ ions in the (3dx2-y2)1 configuration increases and the effective J increases. This overlap of the orbital levels appears to play an important role in the absence of superconductivity in LSNO. © 1991.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Maeno1991322,

title = {Structural, normal-state, and superconducting properties of (La1-xBax-ySry)2CuO4},

author = {Y Maeno and A Odagawa and N Kakehi and T Suzuki and T Fujita},

doi = {10.1016/0921-4534(91)90731-D},

year  = {1991},

date = {1991-01-01},

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

volume = {173},

number = {5-6},

pages = {322-330},

abstract = {We report on the interplay among the structural transitions, transport anomalies and superconductivity in (La1-xBax-y)2 CuO4. For (La1-xBax)2CuO4 y=0, it is now well established that high-Tc superconductivity is suppressed in a narrow range of x around 0.0625. In this study, the amount of doping is held at x=0.0625 and the structural transition temperatures are controlled by a new parameter y. The appearance of the low-temperature tetragonal (TLT) phase and the depression of superconductivity correlate well, but unlike in (La1-xBax)2Cuo4 the transport anomalies can be decoupled from structural transition, implying the presence of a new instability in the electronic state, which precedes the structural transition to the TLT phase. © 1991.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Kato19911994,

title = {Low Temperature Specific Heat of (La1-xSrx)2NiO4+δ},

author = {M Kato and Y Maeno and T Fujita},

doi = {10.1143/JPSJ.60.1994},

year  = {1991},

date = {1991-01-01},

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

volume = {60},

number = {6},

pages = {1994-2001},

abstract = {We studied the low temperature specific heat C of nonsuperconducting oxides (La1_xSrx)2NiO4+δ in a wide range of x up to 0.65, along with the lattice parameters at room temperature, electrical resistivity ρ and magnetic susceptibility χ. We observed the qualitative change in both ρ and χ at x=0.20 ∼ 0.25 corresponding to that in c/a, which is ascribed to the transition from the high-spin to low-spin state of Ni ions. The anomalous hump in C below 10 K was observed. It disappears gradually above x∼0.20 and coincides with the transition of the spin states. However, this hump is well described by a modified Schottky-type contribution and possibly originates from the presence of the two-level system due to a glassy magnetic state. © 1991, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Maeno19917753,

title = {Effects of Th doping on structural and superconductive properties of La2-xBaxCuO4},

author = {Y Maeno and N Kakehi and M Kato and T Fujita},

doi = {10.1103/PhysRevB.44.7753},

year  = {1991},

date = {1991-01-01},

journal = {Physical Review B},

volume = {44},

number = {14},

pages = {7753-7756},

abstract = {The striking suppression of superconductivity of La2-xBaxCuO4 in a narrow range of x around 0.125 is known to be a consequence of a structural transition to a low-temperature tetragonal phase below about 60 K. Study of low-temperature lattice instabilities by x-ray diffraction revealed that in La2-y-xThyBaxCuO4 the development of the low-temperature tetragonal phase, as well as the sharp suppression of superconductivity, is centered at x-y0.125, instead of x0.125. Therefore, the anomalous low-temperature behavior is essentially characterized by the density of carriers rather than local ionic forces, which couples with the lattice instabilities. © 1991 The American Physical Society.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}