Nonlinear planar Hall effect from spin-momentum locking inhomogeneities in topological insulator Bi2Se3

Abstract

Nonreciprocal electrical transport responses arise in materials with broken inversion and time-reversal symmetries [1]. Although these nonlinear magnetoresistance or Hall effects are typically weak compared with their linear analogs, they can be used to probe exotic properties like spin-orbit interaction, spin textures and superconductivity. At the surface of the 3D topological insulator (TI) Bi2Se3, a nonlinear planar Hall effect (NPHE) was reported to exist due to the hexagonally warped spin structures [2]. This NPHE is expected to be small at low carrier densities because the hexagonal warping effect is negligible at the Dirac point. In this study, we observed a similar NPHE in Bi2Se3/CoFeB and magnetic insulator/Bi2Se3 heterostructures. Though with a lower carrier density, the NPHE in these systems is two orders of magnitude larger than the previously reported one. Moreover, the strength of this NPHE scales inversely with carrier density. This suggests that the intrinsic hexagonal warping is not the dominant mechanism for the observed NPHE. Instead, we attribute this large NPHE to the recently proposed extrinsic mechanism based on the interplay between current-induced spin-polarization and scattering from spin-momentum locking inhomogeneities [3]. Our results provide experimental evidence for this new mechanism and show that the NPHE can be enhanced by disorder engineering.  Fig. 1 Nonlinear planar Hall effect in a YIG(2.46m)/Bi2Se3(8nm) sample.  Fig. 2 Carrier density dependence of the nonlinear planar Hall effect.