Canted antiferromagnetic phase of the $\nu=0$ quantum Hall state in bilayer graphene

TL;DR

This paper develops a theoretical framework for the $ u=0$ quantum Hall state in bilayer graphene, identifying the canted antiferromagnetic phase as the insulating state at low electric fields and predicting phase transitions observable experimentally.

Contribution

The study introduces a comprehensive phase diagram for the $ u=0$ state in bilayer graphene, incorporating isospin anisotropy, electric field, and Zeeman effects, and links theoretical phases to experimental observations.

Findings

The insulating $ u=0$ state at low electric field is the canted antiferromagnetic phase.

Predicted phase transitions from CAF and FLP to ferromagnetic phase with metallic edge conductance.

Identified experimental signatures to distinguish phases via magnetic field tilting.

Abstract

Motivated to understand the nature of the strongly insulating $\nu=0$ quantum Hall state in bilayer graphene, we develop the theory of the state in the framework of quantum Hall ferromagnetism. The generic phase diagram, obtained in the presence of the isospin anisotropy, perpendicular electric field, and Zeeman effect, consists of the spin-polarized ferromagnetic (F), canted antiferromagnetic (CAF), and partially (PLP) and fully (FLP) layer-polarized phases. We address the edge transport properties of the phases. Comparing our findings with the recent data on suspended dual-gated devices, we conclude that the insulating $\nu=0$ state realized in bilayer graphene at lower electric field is the CAF phase. We also predict a continuous and a sharp insulator-metal phase transition upon tilting the magnetic field from the insulating CAF and FLP phases, respectively, to the F phase with metallic edge conductance $2e^2/h$, which could be within the reach of available fields and could allow one to identify and distinguish the phases experimentally.