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Quantum and Randomness Effects on Cooperative Phenomena in Spin systems

自旋系统中合作现象的量子和随机性效应

基本信息

批准号：
14540351
负责人：
HTAKAYAMA Hajime
金额：
$ 1.15万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2003
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-14540351/
关键词：
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 (磁場シフト)エイジング

项目摘要

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.

1]利用量子MonteCalro（MC）方法，采用连续虚时间环算法，研究了海森堡反铁磁（HAF）模型，阐明了该模型所表现出的以下新的量子磁现象的机理。1)在二维（2D）HAF模型中引入位置或键稀释时出现的非磁性杂质诱导的Neel长程有序; 2）键交替n腿梯形HAF模型中的量子相变; 3）Neel温度对链间准一维（面间）相互作用（准二维）HAF模型及其在自洽RPA理论中的解释，4）通过对“扭曲序参量”的分析，得到了S=1随机交替键HAF模型的基态相图（3，4的论文现已提交）。2]通过对经典自旋系统的普通MC方法，摘要研究了自旋玻璃中阻挫与随机性共存的老化现象，得到了以下新结果。1)在4D Ising EA（IEA）SG模型中，自旋弛豫过程表现出从临界区到热激活过程的交叉. 2)发现3DIEA-SG模型中温度（T）位移时效过程中的自旋弛豫仅在T位移的幅度小时表现出累积记忆效应，而当T位移相对较大时，它表现出归因于SG相的温度-混沌性质的特殊方面。3)通过对三维IEA-SG模型中的场移时效过程的分析，我们发现，这一结果有力地表明了S相在静磁场下的不稳定性，这是自SG研究早期以来一直存在争议的基本问题之一。