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Probing exotic orders in quantum magnets through Berry phases

通过贝里相探测量子磁体中的奇异有序

基本信息

批准号：
18540386
负责人：
AKIHIRO Tanaka
金额：
$ 2.09万
依托单位：
National Institute for Materials Science
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

项目摘要

(1) We have derived a new effective field theory with a topological term (theta-term) which can detect spin gap phases and quantum phase transitions in antiferromagnets in 2 and 3 spatial dimensions. We expect that this theory, which is a natural generalization of the Haldane-Affleck mapping of 1d antiferromagnets to a nonlinear sigma with a theta-term, can be utilized in the search for exotic spin liquid states.(2) In collaboration with researchers in Santa Barbara and Utah, one of us (MK) has resolved the issue on the theoretical understanding on the nature of the spinon excitations observed experimentally in the 2d compound Cs_2CuCl_4. The theory models the system as composed of weakly coupled antiferromagnetic spin chains, and reproduces well the experimental results. This finding implies that the spinons in this compound are best understood to be descendent s of the conventional spinon excitations which exist in Id. systems.(3) In collaboration with K. Totsuka of the Yukawa Institute, Kyoto University, the Head Investigator of this project investigated the magnetization process of antiferromagnets in an external magnetic field. We found that spacetime vortices of the spin components lying within the plane normal to the field contributes nontrivial Berry phases which doinate the low energy physics. The Berry phase effect reproduces known results for ld, provides natural extensions to 2 and 3d, and also under certain conditionsmaps the system into a lattice gauge theory which gives rise to a novel massive phase characterized by a fractional magnetization plateau.

(1)我们导出了一个新的有效场论，它带有一个拓扑项（θ项），可以在二维和三维空间中探测反铁磁体的自旋能隙相位和量子相变。我们期望，这个理论，这是一个自然的推广的Haldane-Affleck映射的一维反铁磁体的非线性西格玛与θ-项，可以利用在寻找奇异的自旋液体状态。(2)在与圣巴巴拉和犹他州的研究人员的合作中，我们之一（MK）解决了在二维化合物Cs_2CuCl_4中实验观察到的自旋子激发性质的理论理解问题。理论模型的系统组成的弱耦合的反铁磁自旋链，并再现实验结果。这一发现意味着该化合物中的自旋子最好理解为存在于Id.系统中的常规自旋子激发的后代。(3)与K合作。该项目的首席研究员、京都大学汤川研究所的Totsuka研究了反铁磁体在外部磁场中的磁化过程。我们发现，位于垂直于场的平面内的自旋分量的时空涡旋贡献了非平凡的Berry相位，这导致了低能物理。Berry相效应再现了ld的已知结果，提供了对2 d和3d的自然扩展，并且在某些条件下还将系统映射到格点规范理论中，从而产生了一种以分数磁化平台为特征的新型大质量相。