Faculty Profiles - TEI Kokukei

Papers - TEI Kokukei

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NMR study of high-Tc superconductors and related materials

K. Ishida, Y. Tokunaga, Y. Kitaoka, G. Q. Zheng, K. Magishi, H. Mukuda, H. Tou, T. Mito, K. Asayama

Physica B: Condensed Matter 259-261 511 - 516 1999

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

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

DOI： 10.1016/S0921-4526(98)01015-1

Study of spin-ladder system under pressure

T. Mito, K. Magishi, S. Matsumoto, G. Q. Zheng, Y. Kitaoka, K. Asayama, N. Motoyama, H. Eisaki, S. Uchida

Physica B: Condensed Matter 259-261 1042 - 1043 1999

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

High-pressure NMR measurements on a single crystal of hole-doped two-leg ladder compound, Sr2Ca12Cu24O41, have been carried out up to ∼1.7 GPa. The activated T-dependences of T1 and Knight shift at 1.7 GPa assured the persistence of the spin gap in this system. © 1998 Elsevier Science B. V. All rights reserved.

DOI： 10.1016/S0921-4526(98)00807-2

11B NMR of YNi2B2C single crystal in the superconducting state

Guo-Qing Zheng, Y. Wada, K. Hashimoto, Y. Kitaoka, K. Asayama, H. Takeya, K. Kadowaki

Journal of Physics and Chemistry of Solids 59 ( 10-12 ) 2169 - 2172 1998

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier Ltd

We have measured the spin-lattice relaxation rate 1/T1 in an as-grown single crystal of YNi2B2C (Tc = 13.8 K) in the superconducting state down to 0.9 K. 1/T1 shows no Hebel-Slichter peak just below Tc, decreasing sharply as T3, and followed by a slow dependence of 1/T1 ∝ Tat low temperatures. The pairing state is discussed on the basis of T1 result. © 1998 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(98)00205-4

Pressure Effect on the Spin Fluctuations in YMn2 Mn NQR Study

K. Nishikido, C. Thessieu, G. Q. Zheng, Y. Kitaoka, K. Asayama, R. Hauser

Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu 7 626 - 628 1998

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

We report the NQR study on the pressure-induced paramagnetic state in the antiferroinagrietic (AF) intermetal-lic compound YMn2 with the Néel temperature TN=100 K at ambient pressure. Froin the T variation of the nuclear spin-lattice relaxation rate, 56(lJT1) of 55Mn above the critical pressure of 4 kbar, the spin fluctuation feature is found to change below a temperature Taf. At higher temperature than Taf, the nuclear relaxation behavior is well described in terms of the self-consistent renomalized (SCR) spin fluctuation theory for nearly AF metals, whereas below Taf a deviation is significant and 1JT1T exhibits a weak T variation. It is pointed out that Taf coincides with the temperature below which a T2 law in electrical resistivity is valid as expected for a Feimi liquid ground state. We proposed that these features are understood from the standpoint that the development of AF spin fluctuation remains in short-range associated with the singlet formation among Mn spins in each tetrahedron as suggested by the inelastic neutron experiments on Y1−xScxMn2. © 1998, The Japan Society of High Pressure Science and Technology. All rights reserved.

DOI： 10.4131/jshpreview.7.626

NMR study of disorder effect on the superconductivity in Tl2Ba2Ca2Cu3O10

Guo-Qing Zheng, Y. Kitaokaa, K. Asayama, K. Hamada, H. Yamauchi, S. Tanaka

Physica C: Superconductivity and its Applications 282-287 ( 3 ) 1385 - 1386 1997

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

63Cu spin-lattice relaxation rate has been measured in annealed and as-grown samples of Tl2Ba2Ca2CU3O10. We found for the first time that Tc increases as a result of decrease of the residual density of states at the Fermi level due to the improvement of crystal order by annealing. A 2-dimensional d-wave superconductivity model accounts for the increase of Tc of 8K in terms of the change in potential scattering due to crystal imperfection which is likely caused by Tl-substitution of Ca site.

DOI： 10.1016/S0921-4534(97)00785-5

Effect of Structural Disorder on the Superconductivity in Tl2Ba2Ca2Cu3O10

Guo-Qing Zheng, Hayato Wakabayashi, Yoshio Kitaoka, Kunisuke Asayama, Kazuyuki Hamada, Hisao Yamauchi, Shoji Tanaka

Journal of the Physical Society of Japan 66 ( 7 ) 1880 - 1883 1997

Language：English Publishing type：Research paper (scientific journal) Publisher：Physical Society of Japan

The 63Cu spin-lattice relaxation rate has been measured in an annealed sample of Tl2Ba2Ca2Cu3O10 with Tc = 123 K, and compared with that in the previously reported asgrown sample with Tc = 115 K. We found, for the first time, that Tc increases as a result of a decrease in the residual density of states (DOS), Nres, at the Fermi level due to the improvement of crystal ordering by annealing. Based on the T1 result, Nres normalized by the value at Tc, Nres/N0, was found to be reduced from 0.30 to 0.18 after annealing. A 2-dimensional d-wave superconductivity model accounts for the increase of Tc in terms of the change in potential scattering due to crystal imperfection, which is probably caused by Ca/Tl inter-substitution.

DOI： 10.1143/JPSJ.66.1880

Spin-gap behavior in underdoped TlSr2(Lu0.7Ca0.3)Cu2Oy: Cu-63 and Tl-205 NMR studies Reviewed

K Magishi, Y Kitaoka, GQ Zheng, K Asayama, T Kondo, Y Shimakawa, T Manako, Y Kubo

PHYSICAL REVIEW B 54 ( 5 ) 3070 - 3073 1996.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

Measurements of the Knight shift of Cu-63 and the nuclear spin-lattice relaxation rate of Tl-205, (205)(1/T-1), have revealed that TlSr2(Lu0.7Ca0.3)Cu2Oy with T-c = 40 K consisting of the bi-CuO2 layer without the CuO chain is In the underdoped regime with the spin pseudogap, which is evidenced by the significant decrease of (205)(1/T1T) below 120 It far above T-c and the decrease of the Cu-63 spin Knight shift upon cooling. Although the disorder is introduced into the adjacent Ca layers to the CuO2 plane by the substitution of Lu for Ca sites, the spin-gap behavior is presented not to be masked. From this result, it is suggested that the absence of the spin-gap behavior in La2-xSrxCuO4 is neither due to the disorder introduced into the adjacent LaO layers to the CuO2 plane by the substitution of Sr for La sites nor the absence of the CuO chain.

NMR study of local hole distribution, spin fluctuation and superconductivity in Tl2Ba2Ca2Cu3O10

Guo-Qing Zheng, Yoshio Kitaoka, Kunisuke Asayama, K. Hamada, H. Yamauchi, S. Tanaka

Physica C: Superconductivity and its Applications 260 ( 3-4 ) 197 - 210 1996.4

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

63Cu, 17O and 205Tl NMR have been performed in the high-Tc superconductor Tl2Ba2Ca2Cu3O10 whose Tc(max) is 127 K. The hole densities at Cu and oxygen sites in the CuO2 plane have been extracted from the nuclear quadrupole frequency vQ. The striking feature is that the Cu holes are significantly transferred to oxygen site due to strong hybridization between Cu and oxygen. From an analysis of T1 and T2G, it has been found that the spectral weight of the spin fluctuation is transferred to higher energy compared to YBa2Cu3O7, while the magnetic correlation length ξ does not differ much. Thus, it is suggested that the higher Tc is due to higher characteristic energy of spin fluctuations, i.e. the superconductivity is spin fluctuation mediated. The superconducting properties are consistently explained by a d-wave superconductivity model with a finite density of states (DOS) at the Fermi level. We show that the disorder of the Ca/TlO layer caused by the partial inter-substitution of Tl and Ca is responsible for the potential scattering to produce such a DOS. It is found that if such a potential scattering were absent, Tc would go up to 132 K which is quite close to the record Tc realized in the Hg based compound.

DOI： 10.1016/0921-4534(96)00092-5

Cu-63 NMR probe of superconducting properties in HgBa2Ca2Cu3O8+delta: A possible reason for T-c=133K Reviewed

K Magishi, Y Kitaoka, GQ Zheng, K Asayama, K Tokiwa, A Iyo, H Ihara

PHYSICAL REVIEW B 53 ( 14 ) R8906 - R8909 1996.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

Superconducting properties in HgBa2Ca2Cu3O8+delta, with a transition temperature of T-c=133 K, have been investigated by measurements of the nuclear spin-lattice relaxation rate, (63)(1/T-1). It has been found that the T1T=const behavior, observed well below T-c, arises from combined relaxation channels to vortex cores, as well as from a residual density of states (DOS), N-res, at the Fermi level associated with the gapless superconductivity. From the value of T1T=const in the latter channel, the DOS fraction normalized by its value at T-c, N-res/N-Tc, has been deduced to be as small as similar to 0.05. Based on the two-dimensional gapless d-wave model, the T-c reduction rate, Delta T-c/T-c0, is estimated to be as small as 0.02 for N-res/N-0 similar to 0.05. It is pointed out that these measures of the quality of HaBa(2)Ca(2)Cu(3)O(8+delta) explain why T-c reaches such a high value.

Spin correlation and superconductivity in overdoped TlSr2CaCu2O7-δ

K. Magishi, Y. Kitaoka, G. Q. Zhen, K. Asayama, T. Kondo, Y. Shimakawa, T. Manako, Y. Kubo

Czechoslovak Journal of Physics 46 ( 2 ) 1091 - 1092 1996

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

The Gaussian spin-echo decay rate, 1/T2G, of 63Cu, which is related to the antiferromagnetic spin correlation length, ξ, has been measured in overdoped TlSr2CaCu2O7-δ with Tc = 70 K, 52 K, and 10 K. It has been found that the decrease of ξ under a critical value makes the pairing interaction weaken, resulting in the marked suppression in Tc with increasing holes.

DOI： 10.1007/BF02583853

NMR of high Tc superconductors

K. Asayama, Y. Kitanka, G. Q. Zheng, K. Ishida, K. Magishi, T. Mito, Y. Tokunaga

Czechoslovak Journal of Physics 46 ( 6 ) 3187 - 3194 1996

Language：English

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

DOI： 10.1007/BF02548129

93Nb NQR Study in Layered Superconducting 2H-NbSe2

Kenji Ishida, Yoshihiro Niino, Guo-Qing Zheng, Yoshio Kitaoka, Kunisuke Asayama, Tsukio Uhtani

Journal of the Physical Society of Japan 65 ( 7 ) 2341 - 2342 1996

Zn and Ni doping effects on Tc and spin gap behavior in YBa2Cu4O8 and YBa2Cu3O6.6

G. Q. Zheng, T. Odaguchi, Y. Kitaoka, K. Asayama, Y. Kodama, K. Mizuhashi, S. Uchida

Physica C: Superconductivity and its Applications 263 ( 1-4 ) 367 - 370 1996

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

The existence of local moments in both Zn- and Ni-doped YBa2Cu4O8 (Y1248) is confirmed by a Curie-law T-dependence of NMR linewidth and the Cu relaxation at low T. The reduction of Cu-NQR signal intensity in Ni-doped Y1248 suggests that, in contrast to the case of Ni-doped YBa2Cu3O7 (Y1237), the Cu spin correlation around Ni is destroyed. This effect may be responsible for the larger reduction of Tc by Ni-doping than in Y1237. For Cu sites which are away from an impurity by two lattice constants, 1/T1T continues to increase below T*, at which it has a maximum in the non-doped material. The effect in reducing T*, which is sometimes called the spin gap temperature, is much more pronounced in Zn-doped samples, suggesting that the reduction of T* is mainly due to the induction of magnetic moments in the dx 2-y2 orbital, which may modify Cu spin fluctuation.

DOI： 10.1016/0921-4534(96)00083-4

63Cu NMR investigation of HgBa2Ca2Cu3O8+δ

K. Magishi, G. Q. Zheng, Y. Kitaoka, K. Asayama, K. Tokiwa, A. Iyo, H. Ihara

Physica C: Superconductivity and its Applications 263 ( 1-4 ) 375 - 377 1996

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

63Cu NMR measurements have been carried out in HgBa2Ca2Cu3O8+δ (Hg1223) with the highest transition temperature, Tc = 133 K, to date. The narrow NMR spectrum and the small residual density of states (DOS), Nres, at the Fermi level in the superconducting state indicate that the Hg1223 possesses good quality.

DOI： 10.1016/0921-4534(95)00830-6

Magnetic excitation and superconductivity in overdop: A NMR study

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

Physical Review B - Condensed Matter and Materials Physics 54 ( 14 ) 10131 - 10142 1996

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

We report extensive measurements of the Knight shift K, the nuclear spin-lattice relaxation rate 1/(Formula presented), and the Gaussian spin-echo decay rate 1/(Formula presented) of (Formula presented) in overdoped (Formula presented)(Formula presented)(Formula presented) (Tl1212) with (Formula presented) = 70 K, 52 K, and 10 K, in order to elucidate the origin of the reduction in (Formula presented) with increasing holes and to identify the symmetry of the order parameter. In the normal state, it is shown that 1/(Formula presented)T obeys the Curie-Weiss law, pointing to the presence of the antiferromagnetic (AF) spin correlation. From the analyses of 1/(Formula presented) and 1/(Formula presented), it is found that the increase of the hole content in Tl1212 compounds makes the characteristic energy of the AF spin fluctuation around a zone boundary, Q=(π/a,π/a), (Formula presented), transfer to a higher-energy region and concomitantly reduces the magnetic correlation length (Formula presented) significantly. The AF spin correlation is concluded to become less distinct in going from the optimum-doped to the overdoped regime. In the superconducting state, the T dependences of K and 1/(Formula presented) have revealed that the superconductivity is in the gapless regime with a finite density of states at the Fermi level. The NMR results are consistently interpreted in the d-wave model in which the impurity scattering is incorporated in terms of the unitarity limit as demonstrated in most of the high-(Formula presented) cuprates so far. Eventually, the reduction in (Formula presented) from 70 K to 52 K in Tl1212 is concluded to be not due to the impurity effect associated with the oxygen content. In the previous works, the enhancement of (Formula presented) from 93 K in (Formula presented)(Formula presented)(Formula presented) with double (Formula presented) layers to 115-135 K in (Formula presented)(Formula presented)(Formula presented)(Formula presented)(Formula presented) and (Formula presented)(Formula presented)(Formula presented)(Formula presented) with triple (Formula presented) layers was shown to be due to the increase in (Formula presented) with (Formula presented) unchanged appreciably. This finding was compatible with the relationship of (Formula presented)∝(Formula presented)(Formula presented)exp(-1/λ) based on the spin-fluctuation-induced mechanism for the d-wave superconductivity. Within the same scheme, the origin of the marked decrease in (Formula presented) irrespective of increasing (Formula presented) in Tl1212 is proposed to be due to the significant reduction in (Formula presented) which makes the pairing interaction weaken and λ in the above formula reduced. © 1996 The American Physical Society.

DOI： 10.1103/PhysRevB.54.10131

NMR probe of superconducting properties in: A possible reason for K Reviewed

K. Magishi, Y. Kitaoka, G. Zheng, K. Asayama, K. Tokiwa, A. Iyo, H. Ihara

Physical Review B - Condensed Matter and Materials Physics 53 ( 14 ) R8906 - R8909 1996

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

Superconducting properties in (Formula presented), with a transition temperature of (Formula presented) K, have been investigated by measurements of the nuclear spin-lattice relaxation rate, (Formula presented). It has been found that the (Formula presented) behavior, observed well below (Formula presented), arises from combined relaxation channels to vortex cores, as well as from a residual density of states (DOS), (Formula presented), at the Fermi level associated with the gapless superconductivity. From the value of (Formula presented) in the latter channel, the DOS fraction normalized by its value at (Formula presented), (Formula presented), has been deduced to be as small as ∼0.05. Based on the two-dimensional gapless (Formula presented)-wave model, the (Formula presented) reduction rate, (Formula presented), is estimated to be as small as 0.02 for (Formula presented). It is pointed out that these measures of the quality of (Formula presented) explain why (Formula presented) reaches such a high value. © 1996 The American Physical Society.

DOI： 10.1103/PhysRevB.53.R8906

63Cu NMR and NQR studies of high-Tc cuprates under pressure

Guo-Qing Zheng, Takeshi Mito, Yoshio Kitaoka, Kunisuke Asayama, Yasuhiro Kodama

Physica C: Superconductivity and its applications 243 ( 3-4 ) 337 - 341 1995.3

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

The spin-lattice relaxation rate 1/T1 and the Knight shift were measured for La1.85Sr0.15CuO4 and YBa2Cu4O8 under pressure to 1.4 GPa. The results together with the previously reported pressure dependence of the nuclear quadrupole frequency, νQ, give evidence that the local hole distribution changes under pressure. In La1.85Sr0.15CuO4, the hole density in the Cu 3d orbit decreases, accompanying a suppression of the antiferromagnetic spin fluctuation of the low-energy component. In YBa2Cu4O8, by contrast, the spin fluctuation changes little while the total hole number in the CuO2 plane increases. We argue that such changes in the hole distribution are responsible for the Tc increase in the respective compounds. We also found that the so-called "spin-gap" behavior in YBa2Cu4O8 becomes more pronounced under pressure. © 1995.

DOI： 10.1016/0921-4534(95)00029-1

NMR study of strongly correlated electron systems Reviewed

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

PHYSICA B-CONDENSED MATTER 206 ( 1-4 ) 55 - 61 1995.2

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

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 7.6GPa from antiferromagnetic (AF) to superconductivity, are clearly related to that of 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-T-c of 2 K at ambient pressure and the narrowest AI NQR line width, the nuclear-spin lattice relaxation rate, (27)(1/T-1) measured in zero field has been found to obey the T-3 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.

DOI： 10.1016/0921-4526(94)00365-3

Other Link： http://orcid.org/0000-0001-5081-2777

Characteristics of the Spin Fluctuation in Tl2Ba2Ca2Cu3O10

Guo-qing Zheng, Yoshio Kitaoka, Kunisuke Asayama, Kazuyuki Hamada, Hisao Yamauchi, Shoji Tanaka, Hisao Yamauchi

Journal of the Physical Society of Japan 64 ( 9 ) 3184 - 3187 1995

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

We report a 63Cu and 17O NMR study in the high-Tc superconductor Tl2Ba2Ca2Cu3O10 with Tc (max) = 127 K. The results of T1 and T2G reveal that the characteristic energy of the antiferromagnetic spin fluctuation ΓQ is higher than that in YBa2Cu3O7, while the magnetic correlation lengths ξ do not differ much from each other. The high Tc in this compound is thus related to large ΓQ, suggesting that the superconductivity is spin fluctuation mediated. © 1995, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.64.3184

Spin Correlation in High-Tc Cuprate HgBa2Ca2Cu3O8+δ with Tc=133 K—An Origin of Tc-Enhancement Evidenced by 63Cu-NMR Study

Ko-ichi Magishi, Yoshio Kitaoka, Guo-qing Zheng, Kunisuke Asayama, Kazuyasu Tokiwa, Akira Iyo, Hideo Imara

Journal of the Physical Society of Japan 64 ( 12 ) 4561 - 4565 1995

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

The Knight shift, the nuclear spin-lattice relaxation rate, 1/T1, and the transverse relaxation rate, 1/T2G, of 63Cu have been separately measured for the square and the pyramidal CuO2 planes in HgBa2Ca2Cu3O8+δ (Hg1223) with the highest transition temperature, Tc= 133 K to date. From the quantitative analysis of 1/T1 and 1/T2G, it is shown that the product of the staggered susceptibility and the characteristic energy of spin fluctuations around a zone boundary, χQΓQ, for the square CuO2 plane site is larger than that for YBa2Cu3O7 (YBCO7), although that for the pyramidal CuO2 plane site is almost the same. This enhancement of χQΓQ for the square site is considered to be responsible for the higher Tc in Hg1223 than in YBCO7. © 1995, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.64.4561

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