1993 Fiscal Year Final Research Report Summary
Studies on the many-body effect and the metal-insulator transition in electronic system in oxides
| Project/Area Number |
03452076
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Applied materials
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| Research Institution | The University of Tokyo |
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Principal Investigator |
UCHINOKURA Kunimitsu Department of Applied Physics, The University of Tokyo, Professor, 工学部, 教授 (20015564)
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| Co-Investigator(Kenkyū-buntansha) |
MAEDA Atsutaka Department of Pure and Applied Science, The University of Tokyo, Associate Profe, 教養学部, 助教授 (70183605)
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| Project Period (FY) |
1991 – 1993
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| Keywords | oxides / metal-insulator transition / many-body effect / electron correlation |
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| Research Abstract |
(1) Study on the microwave surface impedance of oxide superconductors
To reveal the many-body effects in the superconducting state in the cuprate superconductors, we have constructed an equipment for measuring the surface impedance. We have made a superconducting microwave cavity, which is kept at liquid helium temperature, and only the temperature of the samples is varied. Thus we have succeeded in measuring precisely the temperature dependences of the surface resistance and the surface reactance at the same time. Using this we have succeeded in obtaining the change of the scattering time of the quasi-particles in the superconducting states of YBa_2Cu_3O_7 and Bi_2Sr_2CaCu_2O_y and the anisotropy of the penetration depths in La_<2-x>Sr_xCuO_4. In the superconducting state the scattering probability of the quasiparticles is suppressed more drastically than the extrapolated values from the normal state. This indicates that the scattering mechanism of the quasi-particles is electronic in
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origin and provides an important experimental evidence for understanding the mechanism of the high-T_c superconductivity. As for the microwave response to the direction perpendicular to CuO_2 plane it was proposed that the Josephson-like coupling model holds.
(2) Physical properties of the oxides other than high-T_c superconductors
We have studied the superconducting and other physical properties of Li-Ti-O, Li-Va-O, Ba-(Pb, Bi)-O, Bi-M-Co-O (M=Ca, Sr, Ba), and revealed the similarity and the dissimilarity between these materials and high-T_c superconductors. In particular we have measured the anisotropy of the resistivity of single-crystal Bi_2Sr_3Co_2O_9 and have shown that the ratio of the resistivities parallel and perpendicular to CuO_2 plane is of the order of 10^4.
(3) The magnetic properties of cuprates
The magnetic properties of cuprates were studied in view of the many-body effects of spins. We have measured in detail the temperature dependence of the series of the single-crystal La_2Cu_<1-x>Zn_xO_4. We have deduced the anisotropic susceptibility of these materials on the basis of a theoretical model and fitted the experimental data to this theory. Thus we have succeeded in explaining the change of the magnetic properties due to the substitution of Zn for Cu. Moreover we have discovered a new type of magnetic phase transition (to nonmagnetic state) in CuGeO_3. Less
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