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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反铁磁体中由晶格形变和各向异性引起的量子相变。结果表明，未形变各向同性体系的基态为本课题组提出的HSS态。2.确定了一维S=1XXZ模型的精确基态相图。虽然这一结果在定性上不是新的，但由于它的定量精度，它将作为该领域的标准。3.用密度矩阵重整化群方法研究了混合锯齿键Heisenberg链和其中强键被铁磁键随机取代的Z字键Heisenberg链在饱和磁化强度一半时的平台行为。4.用DMRG方法研究了反铁磁交替键链和均匀链混合物的磁化过程。结果表明，实验磁化强度cu…用实空间重整化群方法重新研究了交换作用大小不同的Fibonacci反铁磁XXZ模型的基态。6.将键算符平均场方法应用于一维锯齿形交替键链的m=1/3平台态，再现了Tonegawa等人得到的相图。7.在周期为-3的S=1/2之字形海森堡模型的M=1/3平台上，证明了经典平台态和量子平台态是不同的相，并且存在一个Z_2对称性破裂的中间相。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，不同的反铁磁相和亚铁磁相的空间调制方式不同。9.在磁场中的准一维量子磁体中，随机性一方面使自旋恢复，导致横向磁序。另一方面，它导致了随机性诱导平台，破坏了磁序。由于这两种机制的竞争，结果表明，随着磁场的增加，该系统经历了多次重入相变。较少