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Theoretical Studies of Low Dimensional Quantum Magnets with Spatial Structures

具有空间结构的低维量子磁体的理论研究

基本信息

批准号：
14540350
负责人：
HIDA Kazuo
金额：
$ 2.3万
依托单位：
Saitama University
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 2005
项目状态：
已结题

项目摘要

1.The quantum phase transitions due to lattice deformation and anisotropy in the S=1 kagome Heisenberg antiferromagnet are investigated. It is shown that the ground state of the undeformed isotropic system is the HSS-state proposed by the present head investigator.2.The quantitatively accurate ground state phase diagram of the one-dimensional S=1 XXZ model is determined. Although the present result is not qualitatively new, it will serve as a standard in this field due to its quantitative accuracy.3.The behavior of the plateau at the half of the saturation magnetization is investigated using the density matrix renormalization group method for the mixed zigzag bond Heisenberg chain and zigzag bond Heisenberg chain in which the strong bonds are randomly replaced by the ferromagnetic bonds.4.The magnetization process of the mixture of the antiferromagnetic alternating bond chain and the uniform chain is investigated using the DMRG method. It is shown that the experimental magnetization cu … More rve obtained by Ajiro and workers is explained results.5.The ground state of Fibonacci antiferromagnetic XXZ model is re-investigated using the real space renormalization group method in the case where the magnitudes of the two exchange interactions are largely different. The ground state phase diagram is obtained and the presence of new universality class is shown.6.The bond operator mean field method is appled to the m=1/3 plateau state of the one-dimensional zigzag alternating bond chain to reproduce the phase diagram obtained by Tonegawa et al. The effect of the interchain interaction is also investigated.7.Among the M=1/3 plateaus of the period-3 S=1/2 zigzag Heisenberg model, it is shown that the classical plateau state and quantum plateau state are different phases and that there exists an imtermediate phase with Z_2 symmetry breakdown. The model with 4-spin interaction with the quantum plateau ground state is also constructed.8.The S【greater than or equal】1 Heisenberg chain with spatially modulated single ion anisotropy D is investigated by numerical diagonalization. It is shown that various antiferromagnetic phases and ferrimagnetic phases appear according to the pattern of the spatial modulation.9.In quasi-one-dimensional quantum magnets in the magnetic field, randomness revives the spins and induces the transverse magnetic order on the one hand. On the other hand, it induces the randomness induced plateau and destroys the magnetic order. As a result of the competition of these two mechanisms, it is shown that this system undergoes multiple reentrant phase transitions with the increase of the magnetic field. Less

1.研究了S=1 kagome Heisenberg反铁磁体中晶格变形和各向异性引起的量子相变。结果表明，未变形各向同性体系的基态是本课题负责人提出的hss状态。确定了一维S= 1xxz模型定量精确的基态相图。虽然目前的结果在质量上不是新的，但由于其数量上的准确性，它将作为这一领域的标准。采用密度矩阵重整群方法研究了混合之字形键海森堡链和强键随机替换为铁磁键的之字形键海森堡链在饱和磁化一半时的平台行为。用DMRG方法研究了反铁磁交替键链和均匀键链混合物的磁化过程。结果表明，实验磁化效果良好，并解释了Ajiro等人的研究结果。利用实空间重整化群方法重新研究了两种交换相互作用的大小有很大差异的Fibonacci反铁磁XXZ模型的基态。得到了基态相图，并证明了新的通用性类的存在。将键算子平均场法应用于一维之字形交替键链的m=1/3平台态，再现了Tonegawa等人得到的相图。研究了链间相互作用的影响。在S=1/2之形海森堡模型的M=1/3个平台中，经典平台态和量子平台态是不同的相，存在一个Z_2对称击穿的中间相。建立了四自旋与量子平台基态相互作用的模型。采用数值对角化方法研究了具有空间调制单离子各向异性D的S【大于或等于】1海森堡链。结果表明，根据空间调制的规律，出现了各种反铁磁相和铁磁相。在磁场中的准一维量子磁体中，随机性一方面恢复了自旋并诱导了横向磁序。另一方面，它诱发了随机诱发平台，破坏了磁秩序。由于这两种机制的竞争，表明该体系随着磁场的增加而经历多次重入相变。少