Unidirectional magnetoresistance in a nonmagnetic topological insulator with hexagonal warping in the surface states.*

Unidirectional magnetoresistance (UMR) was recently observed in various bilayers consisting of a paramagnetic and a ferromagnetic material, arising from the interplay of spin accumulation and spin dependent scattering. In this work [1], we report the emergence of a novel UMR effect in a non-magnetic topological insulator (TI) layer, which scales linearly with the applied electric and magnetic fields. We show theoretically that this UMR originates from the conversion of a nonlinear spin current in the hexagonally warped surface states to a nonlinear charge current. Remarkably, with an out-of-plane magnetic field, the UMR also depends on the orientation of the current with respect to the crystallographic axes, exhibiting a three-fold rotational symmetry around the axis perpendicular to the [111] surface of the TI layer. This unique feature can be used to map the spin texture of the TI surface states based on the angular dependence of the UMR, alternative to ARPES.
[1] P. He, S. S.-L. Zhang, D. Zhu, Y. Liu, Y. Wang, J. Yu, G. Vignale & H. Yang, arXiv:1706.09589.