Faculty Profiles - TEI Kokukei

Papers - TEI Kokukei

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NMR study in novel superconductors: Heavy-fermion system and high-Tc cuprate

Y. Kitaoka, K. Ishida, G. Q. Zheng, H. Tou, K. Magishi, S. Matsumoto, K. Yamazoe, H. Yamanaka, K. Asayama

Journal of Physics and Chemistry of Solids 56 ( 12 ) 1931 - 1935 1995

Language：English Publishing type：Research paper (scientific journal)

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.

DOI： 10.1016/0022-3697(95)00098-4

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

Guo-qing Zheng, Yoshio Kitaoka, Kenji Ishida, Kunisuke Asayama

Journal of the Physical Society of Japan 64 ( 7 ) 2524 - 2532 1995

Language：English Publishing type：Research paper (scientific journal)

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.

DOI： 10.1143/JPSJ.64.2524

NMR-STUDY OF SYMMETRY OF THE SUPERCONDUCTING ORDER-PARAMETER IN HIGH-T-C CUPRATE SUPERCONDUCTOR Reviewed

Y KITAOKA, K ISHIDA, GQ ZHENG, S OHSUGI, K YAMAZOE, K ASAYAMA

PHYSICA C 235 1881 - 1882 1994.12

Magnetic-field enhancement of 63Cu and 17O relaxation rates in the mixed state of YBa2Cu4O8 observation of fermi-liquid state in the vortex cores

Guo-qing Zheng, Yoshio Kitaoka, Kunisuke Asayama, Yasuharu Kodama

Physica C: Superconductivity and its applications 227 ( 1-2 ) 169 - 175 1994.6

Language：English Publishing type：Research paper (scientific journal)

The 63Cu and 17O nuclear spin-lattice relaxation rates in YBa2Cu4O8 have been measured in the temperature and magnetic field ranges of 1.4-270 K and 4.0-11 T, respectively. In the mixed state, 1/T1 for both 63Cu and 17O are enhanced by the magnetic field. Most strikingly, in a high field of 11 T, 63(1/T1) and 17(1/T1) decrease in proportion to the temperature, T, below T=15 K and T=10 K, respectively. The magnetic-field dependence of 1/T1 is shown to be dominated by spin diffusion to the vortex cores, implying that the electronic state in the cores is characterized by the T1T=const. law. This result indicates that the electronic state in the vortex cores is described in terms of the Fermi-liquid picture, in sharp contrast to the unusual properties above Tc. © 1994.

DOI： 10.1016/0921-4534(94)90370-0

Cu NMR and NQR Studies of High-Tc Superconductor La2-xSrxCuO4

Shigeki Ohsugi, Yoshio Kitaoka, Kenji Ishida, Guo-Qing Zheng, Kunisuke Asayama

Journal of the Physical Society of Japan 63 ( 2 ) 700 - 715 1994

Language：English Publishing type：Research paper (scientific journal)

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&gt
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.

DOI： 10.1143/JPSJ.63.700

Pressure dependence of local hole distribution and spin correlation in La1.85Sr0.15CuO4

Guo-qing Zheng, Takeshi Mito, Yoshio Kitaoka, Kunisuke Asayama

Physica C: Superconductivity and its applications 235-240 ( 3 ) 1577 - 1578 1994

Language：English Publishing type：Research paper (scientific journal)

Both 63Cu NQR frequency νQ and 1/T1T were found to decrease under high pressure up to 14kbar, indicating the decrease of hole density at Cu site. The enhancement of Tc under pressure is explained as due to the transfer of hole density from Cu to oxygen, which increases the effective carrier density. © 1994.

DOI： 10.1016/0921-4534(94)92014-1

⁶³Cu NMR study in high-T_c superconductor TlSr₂(Lu_1-xCa_x)Cu₂o_y Reviewed

K. Magishi, G.-q. Zheng, Y. Kitaoka, T. Kondo, Y. Shimakawa, T. Manako, Y. Kubo

Physica C: Superconductivity and its applications 235-240 ( PART 3 ) 1631 - 1634 1994

CU-63 NMR-STUDY OF HEAVILY-DOPED SUPERCONDUCTOR TLSR2CACU2O7-GAMMA Reviewed

GQ ZHENG, K MAGISHI, Y KITAOKA, K ASAYAMA, T KONDO, Y SHIMAKAWA, T MANAKO, Y KUBO

PHYSICA B-CONDENSED MATTER 186-88 1012 - 1014 1993.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The Cu-63 Knight shifts have been measured for the heavily doped high-T(c) superconductors TlSr2CaCu2O7-y, with T(c) = 64 and 45 K. The spin part of the shift, K(s), is almost T-independent in the normal state and increases with decreasing T(c). From the analysis of the anisotropy in K(s) in both compounds, the transferred hyperfine field from the nearest-neighbor Cu spins has been deduced to be larger than that in YBa2Cu3O7, similar to the results for Tl2Ba2CuO6+y. A systematic correlation has been found in the heavily doped superconductors that the spin susceptibility and the nuclear quadrupole frequency increase with decreasing T(c), while 1/T1T is suppressed, as reported previously.

17O NMR study of La2-xSrxCuO4 in the lightly-and heavily-doped regions

G. Q. Zheng, T. Kuse, Y. Kitaoka, K. Ishida, S. Ohsugi, K. Asayama, Y. Yamada

Physica C: Superconductivity and its applications 208 ( 3-4 ) 339 - 346 1993.4

Language：English Publishing type：Research paper (scientific journal)

A 17O NMR study has been carried out for La2-xSrxCuO4 in the lightly- (x=0.075) and heavily-doped (x=0.24) regions in the normal state. Together with the data previously reported for x=0.15, it was found that the nuclear quadrupole frequency νQ in the apical oxygen (O(1)) does not change with x, suggesting that the doped hole does not go into the LaO layer at all. On the contrary, νQ in the planar oxygen (O(2)) increases appreciably with Sr doping. By analyzing νQ of Cu and O(2), it was shown that the increase of holes on the planar O 2pσ orbit is more appreciable than that in the Cu 3d orbit. From the ratio of the hole density in Cu to that in oxygen, and the spin fluctuation probed by 63(T1T), it is suggested that the depression of Tc in the "heavily-doped" region is neither due to the over-doping nor to the collapse of the two-dimensionality, but to other causes. The temperature dependences of the Knight shift 17K in two samples are in sharp contrast with each other. In the lightly-doped region, 17K decreases with decreasing temperature. In the heavily-doped region, however, 17K increases slightly with decreasing temperature, becoming almost T-independent below 100 K. An increase of the anisotropic part of spin Knight shift 17Ks,ani with x also indicates that the hole density at the O 2pσ orbit increases with Sr doping. © 1993.

DOI： 10.1016/0921-4534(93)90206-6

NMR in highly correlated superconductors Reviewed

K. Asayama, Y. Kitaoka, G. q. Zheng, K. Ishida, S. Ohsugi

Hyperfine Interactions 79 ( 1-4 ) 835 - 849 1993.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Kluwer Academic Publishers

Results of our systematic NMR study in high Tc cuprates are reviewed. The antiferromagnetic spin fluctuations (AFSF) decrease in the order of La1.85Sr0.15CuO4. YBa2Cu3O7 and Tl2Ba2CuO6+y. 1/T1 of63Cu in the CuO2 plane in the normal state follows essentially a Curie-Weiss law at high temperature and T1T = const. law at low temperature. The temperature dependence of 1/T1 and the Knight shift together with their impurity effect in the superconducting state strongly suggest d-wave pairing implying the AFSF to be responsible for the occurrence of superconductivity. From the NQR frequency measurement the density of Cu 3d and O 2p holes decreases and increases, respectively, in the order of La, Y and Tl compounds, which is consistent with the change of AFSF. The relation between Tc and vQ, and their pressure dependence suggest that there exists and optimum value of the ratio of Cu 3d and O 2p hole density to give a maximum in Tc. © 1993 J.C. Baltzer AG, Science Publishers.

DOI： 10.1007/BF00567615

NMR and NQR studies of spin correlation and superconductivity in high-Tc oxides

Y. Kitaoka, K. Ishida, G. q. Zheng, S. Ohsugi, K. Asayama

Journal of Physics and Chemistry of Solids 54 ( 10 ) 1385 - 1392 1993

Language：English Publishing type：Research paper (scientific journal)

The magnetic and superconducting properties in high-Tc cuprates have been investigated over a wide doping range by NMR and NQR of 63Cu and 17O in the lightly-doped La2⇔xSrxCuO4] (LSCO), YBa2Cu4O8 (Y124) and the heavily-doped Bi2Sr2CaCu2O8 (BSCO), Tl2Ba2CuO6+y (TBCO) and the Zn- and Ni-doped YBa2Cu3O7 (YBCO7). From extensive studies in the normal state, it is extracted that the uniform, χs(T) and the staggered, χQ(T) susceptibilities originating from the antiferromagnetic (AF) spin correlation are suppressed with increasing hole content and furthermore, the T-dependence of χs(T) and χQ(T) is changed from the T-increasing behavior with temperature and the Curie-Weiss one into the T-independent behavior, respectively. The superconducting properties cannot be accounted for by the conventional BCS model or other isotropic s-wave models. A d-wave model is applicable in interpreting consistently most of NMR results, if the finite density of states at the Fermi level is taken into consideration associated with the pair breaking effect. There are increasing evidences that the magnetic mechanism for the superconductivity is promising in high-Tc cuprates. © 1993.

DOI： 10.1016/0022-3697(93)90198-Z

63Cu NQR/NMR Study of Zn-Substituted YBa2Cu408 -Effect of Impurity on Spin-Gap-Like Behavior-

Guo-Qing Zheng, Takahiro Odaguchi, Yasuharu Kodama

Journal of the Physical Society of Japan 62 ( 8 ) 2591 - 2594 1993

Language：English Publishing type：Research paper (scientific journal)

The nuclear-spin-lattice relaxation rate, 1/Tu and the Knight shift, Kab, of 63Cu in the plane have been measured for YBa2(Cu1-xZnJC)408 (x=0.01 and 0.02) in order to unravel the underlying problem of spin dynamics in YBa2Cu408. It was found that the substitution of Zn into the Cu02 plane causes a continuous increase of 1/TXT down to Tc in contrast to the marked reduction of l/T{Tat far above Tc for the undoped sample, while the Knight shift is invariant. These findings show that the suppression of the spin fluctuation spectral weight around Q=(n, n) at low energies is removed by substituting Zn into the Cu02 plane, while that around q-{0, 0) is not affected appreciably. The ^-dependent change of spin-fluctuations with Zn-doping may be crucial in elucidating the cause of the decrease of 63(l/7,1r) above Tc. © 1993, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.62.2591

NMR IN HIGHLY CORRELATED SUPERCONDUCTORS

K ASAYAMA, Y KITAOKA, GQ ZHENG, K ISHIDA, S OHSUGI

HYPERFINE INTERACTIONS 79 ( 1-4 ) 835 - 849 1993

Language：English Publishing type：Research paper (scientific journal) Publisher：BALTZER SCI PUBL BV

Results of our systematic NMR study in high T, cuprates are reviewed. The antiferromagnetic spin fluctuations (AFSF) decrease in the order of La1.85Sr0.15CuO4. YBa2Cu3O7 and Tl2Ba2CuO6+y. 1/T-1 of Cu-63 in the CuO2 plane in the normal state follows essentially a Curie Weiss law at high temperature and T1T = const. law at low temperature. The temperature dependence of 1/T-1 and the Knight shift together with their impurity effect in the superconducting state strongly suggest d-wave pairing implying the AFSF to be responsible for the occurrence of superconductivity. From the NQR frequency measurement the density of Cu 3d and O 2p holes decreases and increases, respectively, in the order of La, Y and Tl compounds, which is consistent with the change of AFSF. The relation between T-c and v(Q), and their pressure dependence suggest that there exists and optimum value of the ratio of Cu 3d and O 2p hole density to give a maximum in T-c.

17O NMR study of local hole density and spin dynamics in YBa2Cu4O8

Guo-qing Zheng, Yoshio Kitaoka, Kunisuke Asayama, Yasuharu Kodama, Yoshihiro Yamada

Physica C: Superconductivity and its applications 193 ( 1-2 ) 154 - 162 1992.4

Language：English Publishing type：Research paper (scientific journal)

17O NMR has been carried out in YBa2Cu4O8 with Tc = 74 K. The nuclear quadrupole tensors in the oxygen sites were determined and compared with those in other high-Tc cuprates. The hole densities in the oxygen and copper sites have been extracted from νz(O) and νQ(Cu) by assuming that the electric field gradient is dominated by the on-site holes. We propose that the hole distribution (the extent of covalency) between the planar oxygens and copper, which is changed by doping and pressure, is a hidden parameter determining the spin dynamics and the superconducting transition temperature Tc in high-Tc cuprates. It was found that 1/T1T and the Knight shift of the planar oxygens decrease with lowering temperature in the normal state. The nuclear relaxation rates of 17O and 63Cu in the CuO2 plane exhibit different behaviors at temperatures higher than ∼ 120 K, reflecting the different q-window of spin fluctuations, while both of them share the same T-dependence below ∼ 120 K down to 55 K. This scaling of 1/T1 between 17O and 63Cu, which is also seen in YBa2Cu3O7 (Tc = 92 K) and YBa2Cu3O6.63 (Tc = 60 K), seems to be essential for high-Tc superconductivity. © 1992.

DOI： 10.1016/0921-4534(92)90882-D

NQR AND NMR IN HIGH-TC SUPERCONDUCTORS Reviewed

K ASAYAMA, Y KITAOKA, GQ ZHENG

ZEITSCHRIFT FUR NATURFORSCHUNG SECTION A-A JOURNAL OF PHYSICAL SCIENCES 47 ( 1-2 ) 7 - 11 1992.1

Language：English Publishing type：Research paper (scientific journal) Publisher：VERLAG Z NATURFORSCH

Recent NQR and NMR experiments on La2-xSrxCuO4, YBa2Cu3O7, Tl2Ba2CuO6+y and other compounds are reviewed. The antiferromagnetic spin fluctuations decrease in the order of La, Y, Tl compounds. In the normal state the T-dependence of (T1T)-1 is considered to follow the Curie-Weiss law at high temperature and the (T1T) = const law at low temperature. The T dependence of 1/T1 below T(c) suggests strongly d-wave pairing. Correlations of the NQR frequency of Cu-63 and O-17 with the antiferromagnetic spin fluctuations and the superconducting transition temperature are discussed.

CORRELATION BETWEEN TC AND THE HOLE DENSITY AT CU AND OXYGEN Reviewed

GQ ZHENG, E YANASE, K ISHIDA, Y KITAOKA, K ASAYAMA, Y KODAMA, S ENDO

PHYSICA C 185 767 - 768 1991.12

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Dependence of NQR frequency, nu-Q(Cu) on pressure up to 1.3GPa is reported for La1.85Sr0.15CuO4 and YBa2Cu4O8. Correlations are found between some physical quantities and the ratio of the hole density in Cu2 to that in O2(3), n(Cu2)/n(O2, 3) which is extracted from nu-Q's. It is proposed tha there exists an optimum of n(Cu2)/n(O2, 3) for T(c) and that the increase of T(c) under pressure is due to the approach of n(Cu2)/n(O2, 3) to the optimum through the local hole transfer.

O-17 AND CU-63 NMR INVESTIGATIONS OF HIGH-TC SUPERCONDUCTOR LA1.85SR0.15CUO4 WITH TC = 38-K Reviewed

K ISHIDA, Y KITAOKA, GQ ZHENG, K ASAYAMA

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 60 ( 10 ) 3516 - 3524 1991.10

Language：English Publishing type：Research paper (scientific journal) Publisher：PHYSICAL SOCIETY JAPAN KIKAI-SHINKO BUILDING

O-17 and Cu-63 NMR measurements have been made in L1.85Sr0.15CuO4 with T(c) = 38 K. Both O-17 Knight shift and quadrupole tensor were determined from the analyses of the O-17 spectrum of oriented powder. The quadrupole frequencies of the planar oxygen and Cu nuclei are consistently interpreted by the analyses of Hanzawa et al. made in YBa2Cu3O7 with the electric field gradients due to the on-site holes at Cu and O sites. Then the weight factor of the Cu-3d(x2 - y2) and 2p-sigma wave functions are deduced, the latter having the larger weight. From the Knight shifts vs the bulk susceptibility plots, the hyperfine coupling constants for O-17 and Cu-63 were almost the same as those in YBa2Cu3O7. Both shifts decrease significantly below T(c) having residual parts of 63K(ab) = 0.38% and 17K(c) = 0.02% at 4.2 K, which were larger than those in YBa2Cu3O7.

NQR investigation of high Tc superconductors under pressure

Guo-qing Zheng, Etsuya Yanase, Kenji Ishida, Yoshio Kitaoka, Kunisuke Asayama, Yasuharu Kodama, Ritsu Tanaka, Sei Nakamichi, Shoichi Endo

Solid State Communications 79 ( 1 ) 51 - 55 1991

Language：English Publishing type：Research paper (scientific journal)

The pressure dependence of the 63Cu nuclear quadrupole resonance (NQR) frequency, νQ, and Tc have been measured for La1.85Sr0.15CuO4 and YBa2Cu4O8 under high pressure up to 1.3GPa. νQ was found to decrease with increasing pressure in La1.85Sr0.15CuO4, while νQ in the CuO2 plane increases with pressure in YBa2Cu4O8. It is evidenced that charge transfer takes place under pressure. Based on the analysis that νQ arises mainly from the on-site holes, a schematic model relating Tc and the ratio of the in-plane hole concentration in the Cu3d and O2p orbitals, n(Cu)/n(O), is constructed. It is proposed that n(Cu)/n(O) is a primarily important factor governing Tc and that the enhancement of Tc under pressure is due to the change of the ratio approaching the most favorable value (∼1). © 1991.

DOI： 10.1016/0038-1098(91)90478-E

NQR study of high-T_c superconductor TlSr₂CaCu₂O_7-δ Reviewed

G.-q. Zheng, Y. Kitaoka, K. Asayama, T. Kondo, Y. Shimakawa, T. Manako, Y. Kubo

Physica C: Superconductivity and its applications 185-189 ( PART 2 ) 765 - 766 1991

Proximity Effect-Induced Superconductivity and NMR Relaxation in Nb-Cu Multilayers

Guo-Qing Zheng, Yoshio Kitaoka, Yasukage Oda, Kunisuke Asayama, Yoshihisa Obi, Hiroyasu Fujimori, Ryozo Aoki

Journal of the Physical Society of Japan 60 ( 2 ) 599 - 607 1991

Language：English Publishing type：Research paper (scientific journal)

The nuclear spin lattice relaxation rate, T1-l, for 63Cu in zero field from 8 K down to 0.3 K, has been measured in Nb-Cu multilayered thin films where both the Nb- and Cu-layer thicknesses are much smaller compared to the coherence lengths. A BCS-like temperature dependence of T1-1 replaced gradually by a Korringa-law-like one at low temperatures has been found. A dependence of the relaxation on the Cu-layer thickness at low temperatures has also been found. It has been proposed and confirmed by a series of experiments that superconductivity in the Cu-layer induced by the proximity effect has an anisotropic energy gap, reflecting the geometrical feature of a thin film. © 1991, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.60.599

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