1999 Fiscal Year Final Research Report Summary
New ordered states and response to dynamical field of strongly fluctuating quantum systems
| Project/Area Number |
10640368
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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 | The University of Tokyo (1999)
Osaka University (1998) |
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Principal Investigator |
MIYASHITA Seiji The University of Tokyo Department of Applied Physics, Professor, 大学院・工学系研究科, 教授 (10143372)
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| Co-Investigator(Kenkyū-buntansha) |
SAITO Keiji The University of Tokyo Department of Applied Physics, Assistant Professor, 大学院・工学系研究科, 助手
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| Project Period (FY) |
1998 – 1999
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| Keywords | quantum spin system / quantum Monte Carlo / nanoscale magnets / ESR / nonadiabatic transition / photoinduced phasetransition |
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| Research Abstract |
We have investigated the local magnetic structures of quantum spin systems induced by inhomogeneity of the lattice mainly by the quantum Monte Carlo method. In particularly, the S=1/2 doped S=1 antiferromagnetic Heisenberg model (Haldane system), the bond random S=1/2 antiferromagnetic Heisenberg model (gapless system) and the bond alternate S=1/2 antiferromagnetic Heisenberg model (dimer system) with a defect of the alternation. We also investigated the mechanism of ferromagnetism in the itinerant electron system (Hubbard model) and found a new type of mechanism. We also developed a new direct numerical method to study the line shape of ESR in strongly interacting quantum spin systems, and investigate the dynamical shift due to the dipole interaction, anisotropy and DM interactions. We have studied the following phenomena in which the quantum dynamics plays an important role. We investigated the quantum hysteresis phenomena in nanoscale molecular magnets such as Mn12, Fe8 and V15 in the view point of non adiabatic transition. We studied the effects of the environments, such as the phonon, the dipole interaction and hyperfine interactions with the nuclear spins, on the quantum dynamics. In particular, we clarified mechanisms of deceptive non-adiabatic transition at very low temperature, of the parity effect due to the thermally excited states and of the quantum foehn phenomena due to inflow of the heat.
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