Symmetry protected fractional Chern insulators and fractional topological insulators

TL;DR

This paper constructs symmetric wavefunctions for fractional Chern insulators and topological insulators, revealing diverse phases with distinct topological orders influenced by lattice symmetries, and provides a framework for future numerical studies.

Contribution

It introduces a parton-based construction of symmetric wavefunctions for FCI and FTI, characterizing their topological orders and gauge structures, and presents explicit examples on various lattices.

Findings

Multiple FCI and FTI phases with same filling but different topological orders.

Ground state degeneracy calculations for these phases.

Explicit wavefunctions on honeycomb and checkerboard lattices.

Abstract

In this paper we construct fully symmetric wavefunctions for the spin-polarized fractional Chern insulators (FCI) and time-reversal-invariant fractional topological insulators (FTI) in two dimensions using the parton approach. We show that the lattice symmetry gives rise to many different FCI and FTI phases even with the same filling fraction $\nu$ (and the same quantized Hall conductance $\sigma_{xy}$ in FCI case). They have different symmetry-protected topological orders, which are characterized by different projective symmetry groups. We mainly focus on FCI phases which are realized in a partially filled band with Chern number one. The low-energy gauge groups of a generic $\sigma_{xy}=1/m\cdot e^2/h$ FCI wavefunctions can be either $SU(m)$ or the discrete group $Z_m$, and in the latter case the associated low-energy physics are described by Chern-Simons-Higgs theories. We use our construction to compute the ground state degeneracy. Examples of FCI/FTI wavefunctions on honeycomb lattice and checkerboard lattice are explicitly given. Possible non-Abelian FCI phases which may be realized in a partially filled band with Chern number two are discussed. Generic FTI wavefunctions in the absence of spin conservation are also presented whose low-energy gauge groups can be either $SU(m)\times SU(m)$ or $Z_m\times Z_m$. The constructed wavefunctions also set up the framework for future variational Monte Carlo simulations.