Switchable Chern insulator, isospin competitions and charge density waves in rhombohedral graphene moire superlattices

TL;DR

This paper explores various topological, magnetic, and charge density phases in rhombohedral graphene moire superlattices, revealing tunable Chern insulators and competing insulating states driven by external fields and electron polarization.

Contribution

It reports the first observation of a reversible Chern insulator at v=1 and identifies multiple insulating phases at v=2, demonstrating complex phase competition in rhombohedral graphene moire systems.

Findings

Reversible Chern insulator at v=1 with tunable Chern numbers.

Transitions between spin-antiferromagnetic, spin-polarized, and valley-polarized insulators at v=2.

Insulating states at fractional fillings v=1/3, 2/3, and 1/2 under magnetic fields.

Abstract

Graphene-based moire superlattices provide a versatile platform for exploring novel correlated and topological electronic states, driven by enhanced Coulomb interactions within flat bands. The intrinsic tunability of graphene s multiple degrees of freedom enables precise control over these complex quantum phases. In this study, we observe a range of competing phases and their transitions in rhombohedrally stacked hexalayer graphene on hexagonal boron nitride (r-6G/hBN) moire superlattices. When electrons are polarized away from the moire superlattice, we firstly identify a Chern insulator with reversible Chern numbers at v = 1 (one electron per moire cell), attributed to the competition between bulk and edge magnetizations.Then, we detect transitions between three distinct insulating states at v = 2, driven by vertical displacement field D and vertical magnetic field B. These insulating phases are distinguished as spin-antiferromagnetic, spin-polarized, and valley-polarized insulators, based on their responses to parallel and perpendicular magnetic fields. When electrons are polarized toward the moire superlattice, in a device with large twist angle, insulating states appear at v = 1/3 and 2/3 at zero magnetic field, and v = 1/2 in a magnetic field. Our findings reveal a rich interplay of charge, isospin, topology and magnetic field in rhombohedral graphene moire superlattices.