Tunable quantum anomalous Hall octet driven by orbital magnetism in bilayer graphene

TL;DR

This paper reports the discovery of a tunable quantum anomalous Hall effect in bilayer graphene driven by orbital magnetism, exhibiting multiple phases with unique topological and magnetic properties at low temperatures.

Contribution

It demonstrates the existence of an octet of QAH phases in bilayer graphene with tunable Chern numbers, driven by orbital magnetism without magnetic doping or Moire engineering.

Findings

QAH effect observed at small magnetic fields and up to 5 K

Multiple QAH phases with distinct topological orders

Evidence of orbital magnetism as the driving mechanism

Abstract

The quantum anomalous Hall (QAH) effect - a macroscopic manifestation of chiral band topology at zero magnetic field - has only been experimentally realized by magnetic doping of topological insulators (1 - 3) and delicate design of Moire heterostructures (4 - 8). However, the seemingly simple bilayer graphene without magnetic doping or Moire engineering has long been predicted to host competing ordered states with QAH effects (9 - 11). Here, we explore states in bilayer graphene with conductance of 2 e2/h that not only survive down to anomalously small magnetic fields and up to temperatures of 5 K, but also exhibit magnetic hysteresis. Together, the experimental signatures provide compelling evidence for orbital magnetism driven QAH behavior with a Chern number tunable via electric and magnetic fields as well as carrier sign. The observed octet of QAH phases is distinct from previous observations due to its peculiar ferrimagnetic and ferrielectric order that is characterized by quantized anomalous charge, spin, valley, and spin-valley Hall behavior.