Enhancing the stability of a fractional Chern insulator against competing phases

TL;DR

This paper explores how to enhance the stability of fractional Chern insulators by tuning band flatness and Chern number, revealing that higher Chern numbers can significantly increase energy gaps and stabilize FCIs.

Contribution

It demonstrates that bands with higher Chern numbers and finite widths can better stabilize FCIs, and introduces a new real-space density profile tool for phase identification.

Findings

Gap increases by nearly two orders of magnitude for C=2 bands compared to C=1.

Band width can stabilize fractional Chern insulators.

A new method to distinguish FCIs from competing phases.

Abstract

We construct a two-band lattice model whose bands can carry the Chern numbers C=0,pm1,pm2. By means of numerical exact diagonalization, we show that the most favorable situation that selects fractional Chern insulators (FCIs) is not necessarily the one that mimics Landau levels, namely a flat band with Chern number 1. First, we find that the gap, measured in units of the on-site electron-electron repulsion, can increase by almost two orders of magnitude when the bands are flat and carry a Chern number C=2 instead of C=1. Second, we show that giving a width to the bands can help to stabilize a FCI. Finally, we put forward a tool to characterize the real-space density profile of the ground state that is useful to distinguish FCI from other competing phases of matter supporting charge density waves or phase separation.