Nonlinear spin and charge transport in topological insulators

An intriguing property of a three-dimensional topological insulator (TI) is the existence of surface states with spin-momentum locking. We report the discovery of a new type of Hall effect in a TI Bi2Se3 film [1]. The Hall resistance scales linearly with both the applied electric and magnetic fields and exhibits a π/2 angle offset with respect to its longitudinal counterpart, in contrast to the usual angle offset of π/4 between the linear planar Hall and anisotropic magnetoresistance. At variance with the nonlinear Hall effect due to Berry curvature dipole in time-reversal invariant materials, this novel nonlinear planar Hall effect originates from the conversion of a nonlinear transverse spin current to a charge current due to the concerted actions of spin-momentum locking and time-reversal symmetry-breaking, which also exists in other non-centrosymmetric materials [e.g., WTe2 and the 2DEG on the SrTiO3(001) surface] with a large span of magnitude.