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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：
11640366
负责人：
HIDA Kazuo
金额：
$ 1.6万
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：
1999
资助国家：
日本
起止时间：
1999 至 2001
项目状态：
已结题

项目摘要

1. One-dimensional random quantum magnetsUsing the density matrix renormalization group (DMRG) method, we have shown that the Haldane state in spin-1 1-dimensional Heisenterg antiferromagnet is stable against randomness.2. One-dimensional quasiperiodic quantum magnetsUsing DMRG, the ground state of spin-1/2 1-dimensional quasipenodic antiferromagnetic XXZ model is investigated. It is shown that the Fibonacci modulation, which is critical in the XY model, becomes relevant in the presence of the antiferromagnetic Ising interaction and the low energy behavior is modified drastically.The one-dimensional half-filled Fibonacci Hubbard model is investigated using DMRG and perturbational renormalization group method. It is shown that a varity of ground states are realized even in the half-filled case. Experimental observation of these phases is expected using the quantum dot array and other systems. Our results suggest the importance of the strong correlation effect in quasiperiodic systems.3. … More One-dimensional quantum magnets with long spatial periodicityUsing the exact diagonalization method, the ground state and magnetization process of various one-dimensional quantum magnets with long spatial periodicity are investigated and universality class and critical exponents of quantum phase transition are clarified.4. Kagome lattice quantum antiferromagnetGround state and low energy exciatation spectrum of the spin-1 kagomee antiferromagnet which is realized in an organic material are investigated by the exact diagonalization and cluster expansion method. It is shown that both magnetic and non-magnetic excitations have finite energy gaps. The hexagonal singlet solid picture is proposed in which the frustration is fully compensated by quantum fluctuation. It is also shown that a magnetization plateau appears at 1/3 of full magnetization.Future projectsThe project with the same subject is approved and the following investigations are in progress.(1) Magnetization process of random one-dimensional quantum magnets(2) Finite temperature properties of the kagome antiferromagnets(3) Ground state phase diagram of S=1 1-dimensional XXZ model with single-site anisotropy(4) Studies of magnetization plateaux in quasi-1-dimensional and quasi-2-dinensional quantum magnets using the bond operator method Less

1. 利用密度矩阵重整群（DMRG）方法，我们证明了自旋-1维Heisenterg反铁磁体的Haldane态对随机性是稳定的。利用DMRG，研究了自旋1/2的一维准周期反铁磁XXZ模型的基态。结果表明，在XY模型中至关重要的斐波那契调制在反铁磁伊辛相互作用的存在下变得相关，并且低能行为被彻底改变。利用DMRG和微扰重整化群方法研究了一维半填充Fibonacci Hubbard模型。结果表明，即使在半填充的情况下，也可以实现多种基态。期望利用量子点阵列和其他系统对这些相位进行实验观察。我们的结果说明了强相关效应在准周期系统中的重要性。利用精确对角化方法，研究了多种具有长空间周期性的一维量子磁体的基态和磁化过程，明确了量子相变的普适类和临界指数。用精确对角化和团簇展开的方法研究了在有机材料中实现的自旋为1的kagomee反铁磁体的基态和低能激发谱。结果表明，磁激励和非磁激励都具有有限的能隙。提出了六方单线态固体图像，其中量子涨落完全补偿了受挫感。在充分磁化的1/3处出现磁化平台。未来项目同一课题的项目已获批准，以下调查正在进行中。(1)随机一维量子磁体的磁化过程(2)kagome反铁磁体的有限温度特性(3)具有单点各向异性的S=1一维XXZ模型的基态相图(4)利用键算符方法研究准一维和准二维量子磁体的磁化平台