| Co-Investigator(Kenkyū-buntansha) |
NEMOTO Koji Graduate School of Science, Hokkaido University, Professor, 大学院・理学研究科, 助教授 (60202248)
NISHIMORI Hidetoshi Faculty of Science, Tokyo Institute of Technology, Professor, 理学部, 教授 (70172715)
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| Research Abstract |
In this program, by the close collaboration of the researchers in France, US and Japan, as well as of the experimentalists and theorists, the fundamental nature of fluctuation which govern the equilibrium and non-equilibrium dynamics in glassy systems such as spin glasses has been studied. The various subjects in the systems have been individually investigated by the sub-groups (or individual members), and their results have been discussed in the workshops-at Royaumont, France, October 1998, and at Kyoto, October 1999-which all the members participated to look for a common concept(s) on fluctuations in the glassy systems. The main results obtained are as follows.
1) Concerned with the aging phenomena in spin glasses : a) Through the detailed measurement of the thermoremanent magnetization, the spin-glass (SG) correlation length has been extracted and its growth law in aging has been experimentally established (Orbach). b.) In temperature-shift and cycling protocols spin glasses exhibit
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apparently paradoxical phenomena, the 'rejuvenation' and 'memory effect'. A theoretical framework, which is constructed in a viewpoint from the phase space and can explain the phenomena consistently, has been proposed (Bouchaud), and the phenomena are numerically analyzed based on the 'hierarchical random energy model' which is within this framework (Nemoto). c) On the other hand, it has been found that the simulational results on the aging phenomena in the EA model agree well with the predictions from the droplet picture which describes the phenomena in the real spin space.
2) From, comparison of the aging phenomena in disordered ferromagnets or ferroelectrics with those in spin glasses, it has been proposed that the aging dynamics in the former materials is well interpreted as the diffusive motion of domain walls in a medium with random potentials (Bouchaud, Cugliandolo).
3). The following new results have been obtained on phase transitions and nature of fluctuations in glassy systems : an extension of the SG mean-field theory to the statistical computations of information (Nishimori), theories on the chiral-glass transition in vector spin glasses and in high-Tc ceramic superconductors (Kawamura), a new type of phase transition in magnetic and superconductive ceramics (Matsuura), the stretched exponential law in the critical fluctuation common to spin glasses and polymer glasses (Campbell), and the fluctuation measurement which clearly reveals a role of the inhomogeneity on various phase transition in glassy systems (Weissman). Less
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