| Project/Area Number |
11640365
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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 |
物性一般(含基礎論)
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| Research Institution | AOYAMA GAKUIN UNIVERSITY |
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Principal Investigator |
KUBO Kenn Aoyama Gakuin University, College of Science and Engineering, Professor, 理工学部, 教授 (30015862)
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| Co-Investigator(Kenkyū-buntansha) |
MOMOI Tsutomu Tsukuba University, Assistannt, 物理学系, 助手 (80292499)
FURUKAWA Nobuo College of Science and Engineering, Associate Professor, 理工学部, 助教授 (00238669)
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| Project Period (FY) |
1999 – 2000
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| Project Status |
Completed (Fiscal Year 2000)
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| Budget Amount *help |
¥3,100,000 (Direct Cost: ¥3,100,000)
Fiscal Year 2000: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 1999: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Keywords | orbital degeneracy / strongly correlated electron systems / ferromagnetism / mangan oxides / double exchange interaction / Hubbard model / quantum flucvtuations / electrical resistivity / スピン系 / 軌道整列 / 磁化プラトー / フラストレーション / 二重交換相互作用 |
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| Research Abstract |
Following the recent discovery of the colossal magneto-resistance in perovskite mangan oxides there occurred explosional activities in experimental as well as theoretical investigations of the related materials. In these materials the degeneracy of 3d atomic orbitals accompanied by Hund's coupling, anisotropic hopping matrix elements, and Jahn-Teller effect is playing a decisive role. This project aimed to clarify the effects of the orbtal degeneracy on the thermodynamic and transport properties of these materials and predict novel properties. We investigated following subjects :
1) the ground state of the doubly-degenetrate Hubbard model in one dimension
2) the groundstate of the double-exchange model in infinite dimensions
3) electronic states and resistivity in the double exchange model in general dimensions
4) anomalous magnon dispersion in perovskite mangan oxides
5) ferromagnetic phase transitions in the double-exchange model.
We obtained following results :
1) We obtained fundamental u
… More
nderstanding on the conditions for the appearance of ferromagnetism in strongly correlated systems with orbital degeneracy, transport properties in ferromagnetic states, the competition between antiferromagnetism and ferromagnetism and the effects of quantum fluctuations.
In particular we clarified that a) when n (electron number density per site) is between 1 and 2, ferromagnetic state is stable in a wide region of parameters since the so-called double-exchange mechanism is quite effective., b) when n=1 ferromagnetism accompanied by orbital order is stabilized and c) when n<1 the stability of ferromagnetism is strongly affected by the electronic band structure and/or the lattice structure.
2) the T cube law of the resistivity in half metals was theoretically derived.
3) the anomalous magnon dispersion observed in perovskite mangan oxides was theoretically derived in terms of electron-phonon interactions
4) lwe have accomplished large scale quantum Monte Carlo simulations of the double exchange model and estimated the criticall temperature and critical indioes of the ferromagnetic phase transitions. Less
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