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arXiv 0704.3829cond-mat.str-elcond-mat.mes-hallhep-th
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Kitaev型自旋模型中的规范对称性与奇流形上的指标定理

Gauge symmetry in Kitaev-type spin models and index theorems on odd manifolds

Yue Yu

摘要:

构造了蜂窝晶格上的自旋- $\frac{1}2$模型,它是Kitaev模型的推广.通过对该模型的基态区--无涡区的研究,分析了系统的拓扑相。基本上有两个阶段,A阶段和B阶段。通过将基态扇区映射到正方形晶格上具有可调配对参数的无自旋费米子的一般p波配对态,可以研究A相和B相的行为。在这个p波配对态理论中,A相被证明是强配对相,绝缘相。B相可以是带隙或无隙的,这取决于广义反转对称性是否破缺。带隙的B是由无自旋费米子的摩尔-里德-普费米子态或空穴的反普费米子态描述的弱配对相,取决于下一个最近邻跳跃幅度的符号。在带隙的B相中发现了一个介于Pfnanan态和反Pfnanan态之间的相变。此外,我们还证明了在我们的模型中存在一个隐藏的SU(2)规范对称性。在带隙的B相中,基态具有非平凡的拓扑数、光谱第一陈数或手征中心荷,反映了边缘态的手征反常。我们证明了拓扑数是约化的η-不变量,并且通过2+1维的指标定理证明了这种反常可以被SO(3)群的体Wess-Zumino项抵消.

英文摘要:

We construct an exactly soluble spin-$\frac{1}2$ model on a honeycomb lattice, which is a generalization of Kitaev model. The topological phases of the system are analyzed by study of the ground state sector of this model, the vortex-free states. Basically, there are two phases, A phase and B phase. The behaviors of both A and B phases may be studied by mapping the ground state sector into a general p-wave paired states of spinless fermions with tunable pairing parameters on a square lattice. In this p-wave paired state theory, the A phase is shown to be the strong paired phase, an insulating phase. The B phase may be either gapped or gapless determined by the generalized inversion symmetry is broken or not. The gapped B is the weak pairing phase described by either the Moore-Read Pfaffian state of the spinless fermions or anti-Pfaffian state of holes depending on the sign of the next nearest neighbor hopping amplitude. A phase transition between Pfaffian and anti-Pfaffian states are found in the gapped B phase. Furthermore, we show that there is a hidden SU(2) gauge symmetry in our model. In the gapped B phase, the ground state has a non-trivial topological number, the spectral first Chern number or the chiral central charge, which reflects the chiral anomaly of the edge state. We proved that the topological number is identified to the reduced eta-invariant and this anomaly may be cancelled by a bulk Wess-Zumino term of SO(3) group through an index theorem in 2+1 dimensions.

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