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

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.