Local spectroscopy of a gate-switchable moire quantum anomalous Hall insulator

In recent years, correlated insulating states, unconventional superconductivity, and topologically non-trivial phases have all been observed in several moire heterostructures. However, understanding of the physical mechanisms behind these phenomena is hampered by the lack of local electronic structure data. Here, we use scanning tunnelling microscopy and spectroscopy to demonstrate how the interplay between correlation, topology, and local atomic structure determines the behaviour of electron-doped twisted monolayer-bilayer graphene. Through gate- and magnetic field-dependent measurements, we observe local spectroscopic signatures indicating a quantum anomalous Hall insulating state with a total Chern number of & PLUSMN;2 at a doping level of three electrons per moire unit cell. We show that the sign of the Chern number and associated magnetism can be electrostatically switched only over a limited range of twist angle and sample hetero-strain values. This results from a competition between the orbital magnetization of filled bulk bands and chiral edge states, which is sensitive to strain-induced distortions in the moire superlattice. Twisted moire heterostructures offer a highly tunable solid-state platform for exploring fundamental condensed matter physics. Here, the authors use scanning tunnelling microscopy to investigate the local electronic structure of the gate-controlled quantum anomalous Hall insulator state in twisted monolayer-bilayer graphene.

Automated summary

In recent years, various phenomena such as correlated insulating states, unconventional superconductivity, and topologically non-trivial phases have been observed in moire heterostructures. However, the lack of local electronic structure data has hindered the understanding of the underlying physical mechanisms. In this study, scanning tunnelling microscopy and spectroscopy are used to investigate the behaviour of electron-doped twisted monolayer-bilayer graphene, revealing the interplay between correlation, topology, and local atomic structure. The results provide insights into the gate-controlled quantum anomalous Hall insulator state in twisted moire heterostructures.