2001 Fiscal Year Final Research Report Summary
Theoretical Study on the Multiple-exchange Interactions in Two-dimensional Quantum Solids
| Project/Area Number |
10203202
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| Research Category |
Grant-in-Aid for Scientific Research on Priority Areas (B)
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| Allocation Type | Single-year Grants |
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| Research Institution | Aoyama Gakuin University (1999-2001)
University of Tsukuba (1998) |
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Principal Investigator |
KUBO Kenn Aoyama Gakuin University, Department of Physics, Professor, 理工学部, 教授 (30015862)
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| Co-Investigator(Kenkyū-buntansha) |
MOMOI Tsutomu Tsukuba University, Institute of Physics, Reseach Associate, 物理学系, 助手 (80292499)
HATANO Naomichi Aoyama Gakuin University, Department of Physics, Associate Professor, 理工学部, 助教授 (70251402)
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| Project Period (FY) |
1998 – 2000
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| Keywords | ^3He solid layers / multiple-spin exchange / triangular lattice / spin model / chiral phase transition / magnetization plateau / frustration / Monte Carlo method |
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| Research Abstract |
(a) We investigated the groundstate of the spin system on the triangular lattice with 2-(strength J) and 4-spin(strngth K) exchange interactions and obtained following results : (a)The tetrahedral ground state with scalr chirality is realized when the 4-spin exchange is dominant. We investigated the finite temperature phase transition by Monte Carlo simulations and found that the transition is of the first order. (b) We established by means of the mean field theory and the diagnalization of finite clusters that the magnetization curve shows a 1/2-plateau behavior when J/K = -6〜2. We showed that the plateau is realized by uuud state with translational symmetry breaking and and leads to a sharp phase transition at a finite temperature. (c) The 120°Neel state is destabilized by 4-spin exchange interactions at J/K = 10. A novel groundstate with 6 sublattices is stable in a region where J/K < lO. Furthermore we found various novel groundstates with large spatial structures for -8.6 < J/K < -2. We also investigated the effect of the external magnetic field and found that the magnetic field stabilizes several new ground states.
(b) We investiated the incommensurate-commensurate transition in ^3He solid layers. The transition was interpreted as a phase transition of a two-dimensional soliton lattice.
(c) We improved the multicanonical Monte Carlo method and applied it to the 3-dimensional ±J Ising model. Our eresult supports the droplet picture of the spin glass phase.
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