| Project/Area Number |
09640453
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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 | University of Tsukuba |
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Principal Investigator |
KUBO Kenn University of Tsukuba, Institute of Physics, Professor, 物理学系, 教授 (30015862)
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| Co-Investigator(Kenkyū-buntansha) |
MOMOI Tsutom University of Tsukuba, Institute of Physics, Research Associate, 物理学系, 助手 (80292499)
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| Project Period (FY) |
1997 – 1998
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| Project Status |
Completed (Fiscal Year 1998)
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| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1998: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1997: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Keywords | ferromagnetism / itinerant electrons / multiple-band effect / Hurd's rule coupling / double exchange inter-action / Collossal magneto-resistance |
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| Research Abstract |
1. We studied the 1D Hubbard model with two-fold orbital degeneracy by using density matrix renormalization group method, and obtained ground state phase diagram. We obtained perfectly ferromagnetic ground state for n<1, n=1 and n>1 where n denotes the electron density per site. The ferromagnetism for n<1 was shown to be fragile against chay the band dispersion, while that for n>1 is robust.
2. We studied the doubly degenerate Habbard model in infinite dimensions by using the dynamical mean field theory, and to obtained ground stats place diagram. We obtained perfectly ferromagnetic ground state for n=1 and n>1 while we did not find ferromagnetic for n<1. We also found phase separation for n<similar or equal>1 and n<less than o
From above results we established that the Hand's rule coupling which accompanies orbital degeneracy is quite effective in realizing ferromagnetism. Especially the so-called double-exchange mechanism stabilizes metallic ferromagnetism for n>1.
3. We constructed a single-site approximation for the single particle Green's function in the double exchange model. By using this Green's function are calculated the magnetic susceptibility and the electrical conductivity.
4. We obtained the ground state phase diagram of the double exchange model in infinite dimensions taking into account of full quantum effects of spins.
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