Quantum anomalous Hall octet driven by orbital magnetism in bilayer graphene

The quantum anomalous Hall (QAH) effect-a macroscopic manifestation of chiral band topology at zero magnetic field-has been experimentally realized only by the magnetic doping of topological insulators(1-3) and the 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 a conductance of 2 e(2) h(-1) (where e is the electronic charge and h is Planck's constant) that not only survive down to anomalously small magnetic fields and up to temperatures of five kelvin but also exhibit magnetic hysteresis. Together, the experimental signatures provide compelling evidence for orbital-magnetism-driven QAH behaviour that is tunable via electric and magnetic fields as well as carrier sign. The observed octet of QAH phases is distinct from previous observations owing to its peculiar ferrimagnetic and ferrielectric order that is characterized by quantized anomalous charge, spin, valley and spin-valley Hall behaviour(9).

Automated summary

In this study, a state with a conductance of 2e(2)h(-1) in bilayer graphene was discovered, exhibiting magnetic hysteresis and QAH behavior driven by orbital magnetism that can be tuned via electric and magnetic fields. The observed octet of QAH phases in bilayer graphene displays peculiar ferrimagnetic and ferrielectric order characterized by quantized anomalous charge, spin, valley and spin-valley Hall behavior.