Fractional quantum Hall effect in the absence of Landau levels

TL;DR

This paper reports the discovery of fractional quantum Hall effect in a lattice model without Landau levels, showing topological order arising purely from electron interactions in a flat band system.

Contribution

It demonstrates the emergence of FQHE in a lattice model without Landau levels, expanding understanding of topological phases driven by interactions.

Findings

FQHE occurs at 1/3 filling with nearest-neighbor repulsion.

FQHE at 1/5 filling requires next-nearest-neighbor repulsion.

Phase diagram of the topological states is mapped out.

Abstract

It has been well-known that topological phenomena with fractional excitations, i.e., the fractional quantum Hall effect (FQHE) \cite{Tsui1982} will emerge when electrons move in Landau levels. In this letter, we report the discovery of the FQHE in the absence of Landau levels in an interacting fermion model. The non-interacting part of our Hamiltonian is the recently proposed topologically nontrivial flat band model on the checkerboard lattice \cite{sun}. In the presence of nearest-neighboring repulsion ($U$), we find that at 1/3 filling, the Fermi-liquid state is unstable towards FQHE. At 1/5 filling, however, a next-nearest-neighboring repulsion is needed for the occurrence of the 1/5 FQHE when $U$ is not too strong. We demonstrate the characteristic features of these novel states and determine the phase diagram correspondingly.