Bosonic symmetry protected topological phases with reflection symmetry

TL;DR

This paper classifies two-dimensional bosonic SPT phases protected by reflection and local symmetries, revealing their topological classifications and identifying specific models exemplifying these phases.

Contribution

It provides a classification scheme for 2D bosonic SPT phases with reflection symmetry using a Chern-Simons approach, and identifies concrete models like the AKLT state as SPT phases.

Findings

Z_N times R protected phases are _2 imes \u0017_2 for even N

U(1) times R protected phases are _2

The S=2 AKLT state is a _2 SPT phase

Abstract

We study two-dimensional bosonic symmetry protected topological (SPT) phases which are protected by reflection symmetry and local symmetry [$Z_N\rtimes R$, $Z_N\times R$, U(1)$\rtimes R$, or U(1)$\times R$], in the search for two-dimensional bosonic analogs of topological crystalline insulators in integer-$S$ spin systems with reflection and spin-rotation symmetries. To classify them, we employ a Chern-Simons approach and examine the stability of edge states against perturbations that preserve the assumed symmetries. We find that SPT phases protected by $Z_N\rtimes R$ symmetry are classified as $\mathbb{Z}_2\times\mathbb{Z}_2$ for even $N$ and 0 (no SPT phase) for odd $N$ while those protected by U(1)$\rtimes R$ symmetry are $\mathbb{Z}_2$. We point out that the two-dimensional Affleck-Kennedy-Lieb-Tasaki state of $S=2$ spins on the square lattice is a $\mathbb{Z}_2$ SPT phase protected by reflection and $\pi$-rotation symmetries.