2003 Fiscal Year Final Research Report Summary
Quantum and Randomness Effects on Cooperative Phenomena in Spin systems
| Project/Area Number |
14540351
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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 |
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Principal Investigator |
HTAKAYAMA Hajime The University of Tokyo, Institute for Solid State Physics, Professor, 物性研究所, 教授 (40091475)
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| Co-Investigator(Kenkyū-buntansha) |
TOMITA Yusuke The University of Tokyo, Institute for Solid State Physics, Research Associate, 物性研究所, 助手 (50361663)
HUKUSHIMA Koji The University of Tokyo, Department of Basic Science, Associate Professor, 大学院・総合文化研究科, 助教授 (80282606)
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| Project Period (FY) |
2002 – 2003
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| Keywords | Spin glass / Stability of spin-glass states under a static field / Aging phenomena / Temperature-chaos effect / Heisenberg antiferromagnetic model / Quantum Monte Carlo method / Nonmagnetic-impurity-induced antiferromagnetic order / ひねり秩序変数 |
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| Research Abstract |
1]By means of the quantum Monte Calro (MC) method by continuous-imaginary-time loop-algorithm we studied Heisenberg antiferromagnetic (HAF) models and clarified the mechanism of the following novel quantum magnetic phenomena exhibited by the models. 1)The nonmagnetic-impurity-induced Neel long-range order which occurs when site or bond dilution is introduced in the 2-dimensional (2D) HAF model, 2)quantum phase transitions in the bond-alternating n-leg ladder HAF models, 3)the dependence of the Neel temperatures on the interchain (interplane) interactions in the quasi-1D(quasi-2D) HAF models and its interpretation in terms of the self-consistent RPA theory, and 4)the ground-state phase diagram of the S=1 random bond-alternating HAF model by analyzing the "twist order parameter" (the papers for 3,4 are now submitted).
2]By means of the ordinary MC method on classical spin systems, we investigated aging phenomena in spin glasses (SG's) in which frustration and randomness are coexisting, and obtained the following new results. 1)the spin relaxation in the 4D Ising EA (IEA) SG model was found to exhibit the crossover from the critical region to that thermal-activation processes. 2)The spin relaxation in the temperature (T)-shift aging processes in the 3DIEA-SG model was found to exhibit only the cumulative memory effect when a magnitude of the T-shift is small, while it exhibits a peculiar aspect attributable to the temperature-chaos nature of the SG phase when a T-shift is relatively large. 3)Frm analyses of the field-shift aging processes in 3D IEA-SG model, we found the result which strongly suggests the instability of the S phase under a static magnetic field, one of the fundamental issues which has been disputed since the early stage of the SG study.
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Research Products
(10 results)
