Tunable chiral and helical edge state transport in a magnetic topological insulator bilayer

Abstract

The quantum anomalous Hall effect in magnetic topological insulators provides an ideal platform for building topological phases and devices. Here we construct a bilayer structure consisting of two magnetic topological insulator films with drastically different coercive field. In the intermediate field regime, the two quantum anomalous insulators have opposite spin orientation and counter-propagating edge states, thus realizing a synthetic quantum spin Hall phase. Multi-terminal transport measurements show that a moderate magnetic field can tune the system between chiral and helical edge state transport regimes. The interlayer transport realizes quantized spin-biased resistance, and the coupling between the two edges can be tuned by an epitaxially grown spacer layer in a sandwich structure. The tunable chiral and helical edge states in the quantum anomalous Hall bilayer may find unique applications in spintronics and topological quantum computation.