研究者詳細 - 鄭　国慶

論文 - 鄭　国慶

分割表示 265 件中 221 - 240 件目／全件表示 >>

NMR Study of High-Tc superconductors and related materials(共著)

Physica B 259-261 511 - 516 1999年

Study of spin Ladder System under pressure(共著)

Physica B 259-261 1042 - 1043 1999年

¹¹B NMR of Yni₂B₂C single crystal in the superconducting state(共著)

J. Phys. Chem. Solid 59 ( 10-12 ) 2169 - 2172 1998年

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年

記述言語：英語掲載種別：研究論文（学術雑誌）

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

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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年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

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Effect of Structural Disorder on the Superconductivity in Tl₂Ba₂Ca₂Cu₃O₁₀. (共著)

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

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

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

PHYSICAL REVIEW B 54 ( 5 ) 3070 - 3073 1996年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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.

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NMR studies of hole distribution, spin fluctuation and superconductivity in high - Tc superconductor Tl₂Ba₂Ca₂Cu₃O₁₀.(共著)

Physica C 260 ( 3-4 ) 197 - 210 1996年4月

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

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

PHYSICAL REVIEW B 53 ( 14 ) R8906 - R8909 1996年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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.

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Spin correlation and superconductivity in overdoped TISr₂CaCu₂O_7-δ (共著)

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

NMR of high Tc superconductor (共著)

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

⁹³Nb NQR Study in Layered Superconducting 2H-NbSe₂(共著)

J. Phys. Soc. Jpn. 65 ( 7 ) 2341 - 2342 1996年

Zn and Ni doping effects on Tc and spin gap behavior in YBa₂Cu₄O₈ and YBa₂Cu₃O_6.6 (共著)

Physica C 263 ( 1-4 ) 367 - 370 1996年

⁶³Cu NMR Investigation of HgBa₂Ca₂Cu₃O_8+δ (共著)

Physica C 263 ( 1-4 ) 375 - 377 1996年

Magnetic excitation and superconductivity in overdoped TISr₂CaCu₂O_7-δ - A ⁶³Cu NMR study - : (共著)

Physical Review B 54 ( 14 ) 10131 - 10142 1996年

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

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年

記述言語：英語掲載種別：研究論文（学術雑誌）

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

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⁶³Cu NMR and NQR Studies of High-Tc cuprates under Pressure(共著)

Physica C 243 ( 3-4 ) 337 - 341 1995年3月

NMR study of strongly correlated electron systems 査読

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年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

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その他リンク： http://orcid.org/0000-0001-5081-2777

Characteristics of Spin Fluctuation in Tl₂Ba₂Ca₂Cu₃O₁₀. (共著)

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

Spin Correlation in High - Tc Cuprate HgBa₂Ca₂Cu₃O_8+δ with Tc=133K - A Origin of Tc - Enhancement Evidenced by ⁶³Cu - NMR Study - (共著)

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

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