Chern insulators at integer and fractional filling in moiré rhombohedral pentalayer graphene: Part I

The discovery of the fractional quantum anomalous Hall effect in rhombohedral pentalayer graphene (RPG) aligned with hBN sparked substantial interest in this emerging moiré system. Here, we report on our study of an RPG sample with a 10.8 nm hBN moiré. We first focus on a correlated insulating state formed at band filling factor v = 1, arising when electrons are polarized away from the moiré interface with electric displacement field, D. This insulator can be either trivial or topological depending on small changes in D, with corresponding Chern numbers of 0 and +1. The latter state corresponds to an integer quantum anomalous Hall (IQAH) effect arising in the absence of an external magnetic field. Our measurements indicate that the lowest moiré conduction band is not isolated from higher moiré bands, pointing to the possible role of real-space charge ordering in opening a many-body gap and generating an isolated band with integer quantized Berry curvature. In the second part of this presentation we will discuss our observation of an IQAH effect and incipient fractional Chern insulator at fractional band filling v = ⅔.