Interplay of valley, layer and band topology towards interacting quantum phases in moir\'e bilayer graphene

TL;DR

This study investigates how moiré superlattice potentials in bilayer graphene influence topological band structures and quantum phases, revealing complex interplay between valley, layer, and band topology through detailed magnetotransport experiments.

Contribution

It provides experimental evidence of how moiré-induced band topology affects interacting quantum phases in bilayer graphene, highlighting the control of topological states via superlattice engineering.

Findings

Observation of Hofstadter butterfly pattern in Landau fan diagram

Signatures of field-induced correlated insulators and helical edge states

Quantization of interaction-driven topological quantum phases such as Chern insulators

Abstract

In Bernal-stacked bilayer graphene (BBG), the Landau levels give rise to an intimate connection between valley and layer degrees of freedom. Adding a moir\'e superlattice potential enriches the BBG physics with the formation of topological minibands - potentially leading to tunable exotic quantum transport. Here, we present magnetotransport measurements of a high-quality bilayer graphene-hexagonal boron nitride (hBN) heterostructure. The zero-degree alignment generates a strong moir\'e superlattice potential for the electrons in BBG and the resulting Landau fan diagram of longitudinal and Hall resistance displays a Hofstadter butterfly pattern with a high level of detail. We demonstrate that the intricate relationship between valley and layer degrees of freedom controls the topology of moir\'e-induced bands, significantly influencing the energetics of interacting quantum phases in the BBG superlattice. We further observe signatures of field-induced correlated insulators, helical edge states and clear quantizations of interaction-driven topological quantum phases, such as symmetry broken Chern insulators.