Effective field theory for Sp(N) antiferromagnets and their phase structure
Effective field theory for Sp(N) antiferromagnets and their phase structure
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Sp(N)反铁磁体的有效场理论及其相结构
DOI：
10.1103/physrevb.83.174449
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
I. Ichinose
中科院分区：
文献类型：
--
作者：
K. Kataoka;S. Hattori;I. Ichinose
本文利用Schwinger-玻色子表示和路径积分方法研究了量子Sp()反铁磁(AF)海森堡模型。我们同时考虑了消失温度下的二维(2D)系统和有限温度下的3D系统()。导出了有效场论，它是三维CP模型的推广，并用该展开研究了它的相结构。我们还引入了一个与连续介质中的有效场论相对应的CPBoson的格点规范理论模型，并用蒙特卡罗模拟方法研究了它的相结构。对于Sp()模型的特例--2D正方形晶格上的SU()AF磁体，我们在交换耦合中引入了空间各向异性，并证明了随着各向异性的增加，有序Néel态向顺磁相变。另一方面，对于有限情况下的3DSp()系统，我们澄清了整体相结构。随着控制SU()对称性显式破缺的参数的增加，出现了一个类似于受阻SU(2)自旋系统中的螺旋-自旋相的新相。结果表明，在该相变点，在低能区出现了具有复合SU(2)规范场的局域SU(2)规范对称性。这是低能对称性增强现象的又一个例子。由于预期Sp(4)AF磁体是由光学晶格中的冷自旋费米子实现的，上述结果可能在不久的将来得到实验验证。
In this paper, we study quantum Sp() antiferromagnetic (AF) Heisenberg models by using the Schwinger-boson representation and the path-integral methods. We consider both the two-dimensional (2D) system at vanishing temperature and the 3D system at finite temperature (). An effective field theory, which is an extension of the CPmodel in 3D, is derived and its phase structure is studied with theexpansion. We also introduce a lattice gauge theoretical model of CPbosons, which is a counterpart of the effective field theory in the continuum, and study its phase structure by means of Monte Carlo simulations. For SU() AF magnets on the 2D square lattice, which is a specific case of the Sp() model, we introduce a spatial anisotropy in the exchange couplings and show that a phase transition from the ordered Néel state to the paramagnetic phase takes place as the anisotropy is increased. On the other hand for the 3D Sp() system at finite, we clarify the global phase structure. As a parameter that controls explicit breaking of the SU() symmetry is increased, a new phase, which is similar to the spiral-spin phase in frustrated SU(2) spin systems, appears. It is shown that at that phase transition point, a local SU(2) gauge symmetry with composite SU(2) gauge field appears in the low-energy sector. This is another example of the symmetry-enhancement phenomenon at low energies. As it is expected that the Sp(4) AF magnets are realized by cold spin-fermions in an optical lattice, the above results might be verified by experiments in the near future.