Quantum anomalous Hall phases in Bernal stacked bilayer graphene driven by orbital magnetism

The exchange interaction can lead to correlated states in low dimensional systems including the graphene family. Its strength depends in part on the dielectric constant of the surrounding of the system of investigation. Here, we discuss our recent quantum transport epxeriments on high-quality dually-gated bilayer graphene, where the low-k environment leads to comparably large exchange interactions compared to non-suspended samples. Indeed, we have identified clear transport signatures that are consistent with a novel exchange driven quantum anomalous Hall (QAH) nu=2 state that exhibits quantized charge Hall conductance close to zero magnetic field as well as spin, valley and spin-valley anomalous quantum Hall effects and out-of-plane ferroelectricity [1]. The orbital magnetism that leads to the QAH effect arises from the spontaneous chiral symmetry breaking [2].

 

[1] F. R. Geisenhof, F. Winterer, A. M. Seiler, J. Lenz, T. Xu, F. Zhang and R. T. Weitz, "Quantum anomalous Hall octet driven by orbital magnetism in bilayer graphene", Nature 598, 53 (2021)

[2] F. Zhang, Spontaneous chiral symmetry breaking in bilayer graphene. Synth. Met. 210, 9 (2015)