1997 Fiscal Year Final Research Report Summary
Study on Systems with Strong Quantum Fluctuation
| Project/Area Number |
08044081
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| Research Category |
Grant-in-Aid for international Scientific Research
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| Allocation Type | Single-year Grants |
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| Section | Joint Research |
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| Research Field |
物性一般(含基礎論)
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| Research Institution | Osaka University |
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Principal Investigator |
MIYASHITA Seiji Grad.Sch.of Sci.Osaka U.Professor, 大学院・理学研究科, 教授 (10143372)
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| Co-Investigator(Kenkyū-buntansha) |
MIKESKA H.J. ハノバー大学, 教授
TASAKI Haruaki Faculty of Sci.Gakushuin U.Assoc.Prpfessor, 理学部, 助教授 (50207015)
TAKAHASHI Minoru ISSP Tokyo U.Professor, 物性研究所, 教授 (40029731)
TONEGAWA Takashi Faculty of Sci.Kobe U.Professor, 理学部, 教授 (80028167)
SHIBA Hiroyuki Faculty of Sci.Tokyo Inst.Tech.Professor, 理学部, 教授 (30028196)
MIKESKA Hans-Juergen Inst.for Theor.Phys.Hannover U.Professor
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| Project Period (FY) |
1996 – 1997
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| Keywords | quantum fluctuation / singlet pair / tunnel phenomena / quantum phase transition / itinerant ferromagnetism / flutband |
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| Research Abstract |
We have studied systems with strong quantum fluctuation in order to find new peculiar properties due to the quantum mechanical effects. We investigate the effects due to the structure of the lattice on the ordering configuration in the Heisenberg antiferromagnets. Here 'ordering configuration' means the configuration of singlet bonds which is classified with the VBS picture. In particular we investigated a chain which consists of two of S = 1 spins and two of S = 1/2 spins.
We investigated effects of inhomogeneity on quantum mechanical order. In particular, we study the effect of random coupling in S = 1 chain, effects of impurities of S = 1/2 spins and effects of dilution on the ladder lattice and square lattice. In the last project, we find so-called quantum Griffiths phase where the any correlation in the spatial direction decays exponentially but the correlation in the time axis diverges. This divergence causes the divergence of the local susceptibility.
We studied a new phase due to the quantum fluctuation in the magnetization curve in the ground state of antiferromagnetic Heisenberg model with XY anisotropy. There a collinear configuration which is unfavorite in classical case becomes stable. The transition is clearly observed by investigating the wavefunction although the transition is not clear in the changes of physical quantities.
We investigated the low temperature properties of quantum spin systems by quantum Monte Carlo method, transfer matrix method and Bethe anzatz method. We found a new mechanism of the ferromagnetism in the Hubbard model and analyzed the nature of the ferromagnetism.
We also started to study the dynamics of system where the quantum fluctuation has a dominant role.
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