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arXiv 1111.6816cond-mat.str-elhep-th
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三维分数拓扑绝缘体模型

Models of three-dimensional fractional topological insulators

Joseph Maciejko, Xiao-Liang Qi, Andreas Karch, Shou-Cheng Zhang

摘要:

时间反演不变的三维拓扑绝缘体可以基本上由拓扑场论定义,量子化的轴子角θ为零或π。最近的研究表明,分数量子化的θ值与时间反演不变性是一致的,如果deconfined,gapped,分数带电体激发出现在低能量谱由于强相关效应,导致分数拓扑绝缘体的概念。这些分数电荷激发耦合到紧急规范场,确保微观自由度,原始电子,规范不变的对象。构建分数拓扑绝缘体微观模型的第一步是理解这些涌现的规范理论及其相应相的性质。在这项工作中,我们表明,无论是阿贝尔或非阿贝尔类型的低能有效规范理论是与分数量子化的轴子角,如果他们承认一个库仑相或希格斯相与规范群分解到一个离散的子群是一致的。库仑相支持无隙但电中性的体激发,而希格斯相是完全有隙的。Higgs相和非Abel库仑相在具有非平凡第一同调的无边界空间三维流形上表现出多个基态,而Abel库仑相具有唯一的基态.由于诱导边界Chern-Simons项的存在,在有边界流形上基态简并度得到了额外的贡献。

英文摘要:

Time-reversal invariant three-dimensional topological insulators can be defined fundamentally by a topological field theory with a quantized axion angle theta of zero or pi. It was recently shown that fractional quantized values of theta are consistent with time-reversal invariance if deconfined, gapped, fractionally charged bulk excitations appear in the low-energy spectrum due to strong correlation effects, leading to the concept of a fractional topological insulator. These fractionally charged excitations are coupled to emergent gauge fields which ensure that the microscopic degrees of freedom, the original electrons, are gauge-invariant objects. A first step towards the construction of microscopic models of fractional topological insulators is to understand the nature of these emergent gauge theories and their corresponding phases. In this work, we show that low-energy effective gauge theories of both Abelian or non-Abelian type are consistent with a fractional quantized axion angle if they admit a Coulomb phase or a Higgs phase with gauge group broken down to a discrete subgroup. The Coulomb phases support gapless but electrically neutral bulk excitations while the Higgs phases are fully gapped. The Higgs and non-Abelian Coulomb phases exhibit multiple ground states on boundaryless spatial 3-manifolds with nontrivial first homology, while the Abelian Coulomb phase has a unique ground state. The ground state degeneracy receives an additional contribution on manifolds with boundary due to the induced boundary Chern-Simons term.

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