Nonlinear spintronics with inversion symmetry breaking

Spin-orbitronics, which takes advantage of spin-orbit coupling (SOC), has expanded the research objects of spintronics to nonmagnetic materials. Here, we explore the emerging nonlinear spintronic phenomena in the inversion-asymmetric nonmagnetic materials with SOC. The surface state of three-dimensional topological insulator (TI) owns helical spin textures with the spin and momentum perpendicularly locked. We reported the observation of a nonlinear magnetoresistance (called bilinear magneto-electric resistance, BMER) [1] and nonlinear Hall effect [2] in a prototypical TI Bi₂Se₃, which scale linearly with both the applied electric and magnetic fields. A close link between the BMER and the spin texture was established in TI surface states, which enables a novel transport probe of spin textures. We further extended the observation of BMER effect to the d-orbital two-dimensional electron gas (2DEG) at a SrTiO₃ (STO) (111) surface [3]. The BMER probes a three-fold out-of-plane spin texture, in addition to an in-plane one at the STO(111) surface 2DEG. This novel spin texture is in contrast to the conventional one induced by the Rashba effect. We recently reported the observation of nonlinear magnetoresistance at room temperature in a semimetal WTe₂ [4]. Theoretical calculations revealed the critical role of Fermi surface topology and convexity on the nonlinear magneto-response. This novel nonlinear effect originates from the conversion of a nonlinear spin current to a charge current. These findings open a new branch in spintronics, ' nonlinear spintronics', which discusses the nonlinear transport effects in spin-polarized nonmagnetic materials.
References:
[1] Pan He, et al. Nature Physics 14, 495 (2018)
[2] Pan He, et al. Phys. Rev. Lett. 123, 016801 (2019)
[3] Pan He, et al. Phys. Rev. Lett. 120, 266802 (2018)
[4] Pan He, et al. Nature commun., 10, 1290 (2019)