Origin of the unidirectional and bilinear magnetoresistance in topological insulator/ferromagnet heterostructures

Unidirectional magnetoresistance (UMR) has been observed in heavy metal/ferromagnet (HM/FM) [1] and magnetic topological insulator (TI) [2] heterostructures. In both systems, magnon scattering (MS) is shown to play a significant role. However, whether the MS-UMR in these two systems share the same origin remains unclear. On the other hand, bilinear magnetoresistance (BMR) [3] was also reported in the topological insulator Bi₂Se₃, and several mechanisms including hexagonal warping, particle-hole asymmetry, and spin-orbit inhomogeneities have been revealed or proposed. In this study, we observed both UMR and BMR in various TI/FM heterostructures. By using an insulating magnetic layer, we clearly distinguish the MS-UMR in HM/FM and TI/FM as two different mechanisms. By further depositing Bi₂Se₃ on magnetic and nonmagnetic substrates, we show that the UMR and BMR in TI/FM originate from magnetic-proximity-effect-induced band distortion and nonlinear spin-to-charge conversion under time-reversal symmetry breaking conditions.

 

[1] C. O. Avci et al, Nat. Phys. 11, 570 (2015).

[2] K. Yasuda et al, Phys. Rev. Lett. 117, 127202 (2016).

[3] P. He et al, Nat. Phys. 14, 495 (2018).