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A Characterization of Topological Insulators: Chern Numbers for a Ground State Multiplet

Yasuhiro Hatsugai
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Abstract

We propose to use generic Chern numbers for a characterization of topological insulators. It is suitable for a numerical characterization of low dimensional quantum liquids where strong quantum fluctuations prevent from developing conventional orders. By twisting parameters of boundary conditions, the non-Abelian Chern number are defined for a few low lying states near the ground state in a finite system, which is a ground state multiplet with a possible (topological) degeneracy. We define the system as a topological insulator when energies of the multiplet are well separated from the above. Translational invariant twists up to a unitary equivalence are crutial to pick up only bulk properties without edge states. As a simple example, the setup is applied for a two-dimensional $XXZ$-spin system with an ising anisotropy where the ground state multiplet is composed of doubly almost degenerate states. It gives a vanishing Chern number due to a symmetry. Also Chern numbers for the generic fractional quantum Hall states are discussed shortly.

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Yasuhiro Hatsugai. 2004-12-14. A Characterization of Topological Insulators: Chern Numbers for a Ground State Multiplet. https://doi.org/10.1143/jpsj.74.1374

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