| Project/Area Number |
15540357
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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 |
Mathematical physics/Fundamental condensed matter physics
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| Research Institution | Iwate University |
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Principal Investigator |
SHIRAKURA Takayuki Iwate University, Faculty of Humanities and Social Sciences, Professor, 人文社会科学部, 教授 (90187534)
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| Co-Investigator(Kenkyū-buntansha) |
MATSUBARA Fumitaka Tohoku university, Department of Applied Physics, Professor, 工学部, 教授 (90124627)
SHINDO Kouichi Iwate University, Faculty of Humanities and Social Sciences, Professor, 人文社会科学部, 教授 (10004384)
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| Project Period (FY) |
2003 – 2004
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| Project Status |
Completed (Fiscal Year 2004)
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| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 2004: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 2003: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Keywords | spin glass / Monte Carlo simulation / random spin system / Heisenberg model / frustration / replica symmetry breaking |
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| Research Abstract |
We have studied the phase transition of the ±J Heisenberg model in three dimensions. Using the exchange Monte Cairo method, we have investigated the spin-overlap distribution near the SG transition temperature. By selecting the order parameter as the maximum value of the spin overlap of the diagonal componentsunder the uniform rotations, the calculated overlap distribution suggests the appearance of a peculiar type of replica-symmetry breaking which is similar to the one found in the chirality-overlap distribution by Hukushima and Kawamura. This result may explain absence of any crossing of the Binder parameter of the spin at a finite SG transition temperature.
We have also studied the ground state and low-lying excitations of the ±J Heisenberg model on a three dimensional L×L×L (L≦11) lattice. We found evidence of occurrence of a Parisi state. That is, there exists a metastable state with a finite energy of ΔE〜O(J) in the thermodynamic limit and the energy barrier ΔW between the metastable state and the ground state is ΔW∝JL^θ with θ〜0.53. We also found that the energy ΔE of small scale excitations are related to a scale of the excitation V in a similar manner to those of the ferromagnetic model, i. e., ΔE∝J L^ΦV^Ψ with Φ〜-4.7 and Ψ〜2.0. This fact suggests that similarity exists in the ground state structure between the ±J and the ferromagnetic Heisenberg models, though the spin directions of those two models differ greatly from one another.
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