Fractional fractal quantum Hall effect in graphene superlattices

TL;DR

This study reports the observation of fractional quantum Hall states within the Hofstadter spectrum of graphene superlattices, revealing novel many-body states at fractional Bloch fillings not predicted by existing theories.

Contribution

First experimental observation of fractional quantum Hall states in the full Hofstadter spectrum of graphene superlattices, indicating new many-body phenomena.

Findings

Coexistence of fractional and integer QHE states in graphene superlattices

Discovery of new fractional states at large magnetic fields

Fractional Bloch band QHE states not explained by current theories

Abstract

The Hofstadter energy spectrum provides a uniquely tunable system to study emergent topological order in the regime of strong interactions. Previous experiments, however, have been limited to the trivial case of low Bloch band filling where only the Landau level index plays a significant role. Here we report measurement of high mobility graphene superlattices where the complete unit cell of the Hofstadter spectrum is accessible. We observe coexistence of conventional fractional quantum Hall effect (QHE) states together with the integer QHE states associated with the fractal Hofstadter spectrum. At large magnetic field, a new series of states appear at fractional Bloch filling index. These fractional Bloch band QHE states are not anticipated by existing theoretical pictures and point towards a new type of many-body state.