| Project/Area Number |
13640350
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
固体物性Ⅱ(磁性・金属・低温)
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| Research Institution | KYOTO UNIVERSITY (2002-2003)
University of Tsukuba (2001) |
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Principal Investigator |
TSUNETSUGU Hirokazu Kyoto University, Yukawa Institute for Theoretical Physics, Professor, 基礎物理学研究所, 教授 (80197748)
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| Co-Investigator(Kenkyū-buntansha) |
求 幸年 筑波大学, 物質工学系, 助手 (40323274)
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| Project Period (FY) |
2001 – 2003
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| Project Status |
Completed (Fiscal Year 2003)
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| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 2003: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2002: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2001: ¥800,000 (Direct Cost: ¥800,000)
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| Keywords | Strongly Correlated Electrons / Frustration / Quantum Antiferromagnet / Orbital Order / Spinets / Pyrochlore Lattice / Kagome Lattice / パイクロア格子 / 多バンドハバード模型 / 幾何学フラストレーション / 軌道自由度 / 磁性体 / 動的平均場 / 重い電子系 |
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| Research Abstract |
In this project, we have theoretically investigated low-temperature physical properties of magnets with geometrical frustfation, in particular, pyrochlore and Kagome systems. The central issue is the problem of how geometrical frustration affects strong electron correlations in these systems, and quest of novel quantum phase driven by the interplay of quantum fluctuations and geometrical frustration.
We have studied quantum Heisenberg model on the pyrochlore lattice in the quantum limit (S=1/2) and the semiclassical limit (S -> infinity). It is found that when S=1/2, the ground state has a long-range order of two types of dimers or tetramers, accompanied by two spin-singlet excitations. The presence of energy hierarchy is a manifestation of frustration effects, and the ratio of different energy scales is set by geometrical features of the systems.
We have also studied the heavy-fermion behavior in lithium vanadium spinets. To this end, we have employed the Hubbard model on the pyrochlore lattice with taking account of 3-fold orbital degeneracy in vanadium ions. The correlation effects are included within the RPA level. We have found that the enhanced fluctuations of coupled spin and orbital degrees freedom have a character of strong localization in space, which may be a partial answer to the origin of the heavy-fermion behavior. This was then followed by the study on the Hubbard model on the Kagome lattice. We have employed the FLEX approximation in this case. With switching on frustration effects, the SDW instability is strongly suppressed and at the same time, the single-electron spectral function shows a noticeable recovery of coherence in electron dynamics. This is important to stabilize a metalic phase in these system.
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