Spin-Valley Polarized Quantum Anomalous Hall Effect and a Valley-Controlled Half Metal in Bilayer Graphene

TL;DR

This paper uncovers a novel spin-valley polarized quantum anomalous Hall insulator in bilayer graphene, revealing unique edge states and a bulk half-metal phase influenced by magnetic, electric, and optical effects.

Contribution

It introduces the spin-valley polarized quantum anomalous Hall state in bilayer graphene, combining analytical Chern number calculations with edge state analysis under external fields.

Findings

Discovery of the SVP-QAH insulator state at finite bias and light intensity.

Identification of a bulk half-metal state with Berry's phase 2π.

Observation of a spin rectification effect at domain walls.

Abstract

We investigate topological phases of bilayer graphene subject to antiferromagnetic exchange field, interlayer bias, and irradiated by light. We discover that at finite bias and light intensity the system transitions into a previously unknown spin-valley polarized quantum anomalous Hall (SVP-QAH) insulator state, for which the subsystem of one spin is a valley Hall topological insulator (TI) and that of the other spin is a QAH insulator. We assess the TI phases occurring in the system by analytically calculating the spin-valley dependent Chern number, and characterize them by considering edge states in a nanoribbon. We demonstrate that the SVP-QAH edge states lead to a unique spin rectification effect in a domain wall. Along the phase boundary, we observe a bulk half-metal state with Berry's phase of 2\pi.