Fractionalization and Entanglement of High Chern Insulators

TL;DR

This paper reports the discovery of high Chern number states and an exotic fractional Chern insulator in moire flat band systems of layered graphene, expanding the understanding of topological phases and anyonic excitations.

Contribution

It introduces a new moire graphene platform exhibiting high Chern numbers and an unconventional fractional Chern insulator beyond existing theories.

Findings

Observation of Chern insulators with C = 3 to 7

Detection of an exotic fractional Chern insulator with C = 7/3

Demonstration of quantum anomalous Hall effect in these states

Abstract

The realization of fractional Chern insulators opens up the possibility of exploring fractionally charged excitations and anyonic statistics in the absence of a magnetic field. One of the central questions is whether lattice-based systems can give rise to radically new states, distinct from those observed in traditional fractional quantum Hall systems. In this work, we investigate a new type of moire flat band system composed of Bernal bilayer graphene and rhombohedral tetralayer graphene. First, we discover an unprecedented richness of states with high Chern numbers. At v = 1 moire filling, we observe Chern insulators with Chern numbers C = 4 and 3. Flanking v = 3 state, we observe a series of Chern insulators from C = 2 to C = 7. All of these states exhibit the quantum anomalous Hall effect. Remarkably, we observe an exotic fractional Chern insulator with C = 7/3 around v = 2/3 which is beyond all known fractional Chern insulators described by either the Jain sequence as or current high Chern theory. Our work expands the understanding of fractionally charged excitations beyond the Landau level basis and offers a new moir\'e platform for exploring anyons.