| Co-Investigator(Kenkyū-buntansha) |
ZITTARTZ J. University of Cologne, 教授
WOLFLE P. University of Karlsruhe, 教授
VOLLHARDT D. Technical University of Aachen, 教授
MULLER-HARTMANN E. University of Cologne, 教授
福山 秀敏 東京大学, 大学院・理学系研究科, 教授 (10004441)
斯波 弘行 東京工業大学, 理学部, 教授 (30028196)
KAWAKAMI N. Kyoto University, 基礎物理学研究所, 助教授 (10169683)
FUKUYAMA H. The University of Tokyo
SHIBA H. Tokyo Institute of Technology
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| Research Abstract |
This international research project has enabled us not only to discuss on members' results so far obtained, but to initiate new cooperative researches. By this systematic cooperation, we are in the course of building a common global point of view which is based on results from different but related systems and methods.
Concerning the results of research for this year, we have published many papers and are working on new topics which will be published in the next year. Here we report on some of the results.
(1)Concerning the nature of simple excitation spectra in the supersymmetric t-J model extended to SU(N) digress of freedom, a clear insight has been gained by noting that the permutation property of the Gutzwiller wave function is the same as that of free electrons (Kuramoto). In the Sutherland model with special choice of interaction strength, the system gets a similarity to edge states in the fractional quantum Hall (FQH) system (Kawakami). We have proposed a new chiral model in this
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line and derived its exact properties (Kawakami and Kuramoto) In the one-dimensional Anderson lattice, special choice of the parameters can lead to the exact solution (Vollhardt). Furthermore, we have proposed a new supersymmetric continuum model and its exact solution (Kuramoto and Zittartz). Especially for the last study, the research trip by this program was indispensable.
(2)In the limit of high dimensions, the Hubbard model is regarded as an effective Anderson impurity in a self-consistent medium. Impurity effects in this limit has been studied by a rigorous method (Vollhardt). With use of the numerical renormalization group method (NRG), quantities such as the density of states, susceptibility, specific heat has been calculated and a new energy scale has been identified near the metal-insulator transition (Kuramoto).
(3)Dynamics of the two-dimensional t-J model has been studied on the basis of the RVB picture. The dynamical susceptibility has been calculated with use of the slave-boson mean-field theory both above and below the superconducting transition (Fukuyama). The results reproduce experimental results of neutron scattering. Further study beyond the mean-field theory has been initiated with account of fluctuations (Woelfle).
(4)Survey of results has been given on magnetic impurities in a superconductor with use of the NRG (Shiba). Relationship with previous approximate theories has been clarified (Shiba, Mueller-Hartmann, Zittartz). In order to discuss the occurrence of ferromagnetism on a rigorous ground, the ground state of the Hubbard model with slight holes has been studied with special attention to the influence of lattice types (Mueller-Hartmann). Less
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