Orbital Chern Insulators in van der Waals Moiré Systems

Introduction

Topological electronic phases manifest fascinating phenomena, including electronic transport via topologically-protected edge states, anomalous responses to external fields, and excitations with anyonic statistics. Harnessing these phenomena in electronic devices will lead to a technological breakthrough. The main obstacle to this has been the lack of topological systems that are simultaneously clean, versatile, robust, and highly tunable. We argue that the recent discovery of orbital Chern insulators (OCI) in graphene moiré heterostructures opens an exceptional opportunity to make a leap in our ability to manipulate topological electronic phases.

Background

Recently, moiré superlattices in van der Waals materials emerged as a powerful tool to realize correlated electronic phases. The exciting discovery of intrinsic quantum anomalous Hall effects in graphene moiré systems revealed interaction-driven orbital Chern insulating states at zero magnetic field.

Unique Properties of OCIs

Unlike in most known magnets, the magnetism in OCIs arises predominantly from the orbital motion of the electrons rather than their spins, endowing them with unique properties. Remarkably, the moiré heterostructures hosting OCIs could also be gate-tuned to:

1. Superconducting states
2. Correlated insulating states
3. Metallic isospin-ferromagnetic states

These unique features of OCIs set them apart and warrant their thorough investigation.

Objectives

This proposal aims to establish the fundamental properties of OCIs, focusing on three key questions:

1. What are the phase diagram, isospin order, and thermodynamics of OCIs?
2. What is the physics of the chiral edge states and domain walls in OCIs?
3. Can strong interactions in flat moiré bands lead to fractional quantum anomalous Hall effect?

To address these questions, we will apply a combination of complementary experimental techniques to probe electronic transport and thermodynamic properties in high-quality graphene moiré devices.