Spin-orbitronics, which takes advantage of spin-orbit coupling (SOC), has expanded the research objects of spintronics to nonmagnetic materials. Here, we report the emerging nonlinear spintronic phenomena in the inversion-asymmetric nonmagnetic materials with SOC. We show the observation of a nonlinear magnetoresistance (called bilinear magnetoelectric resistance, BMR) and nonlinear Hall effect in a prototypical topological insulator Bi2Se3 [1,2] and Weyl semimetal WTe2 . We further reveal that these effects are originated from the conversion of a nonlinear spin current to charge current under the application of an external magnetic field. A close link between the BMR and the spin texture was established, which enables a novel transport probe of spin textures. We further extended the observation of BMR effect to the two-dimensional electron gas (2DEG) at a SrTiO3 (STO) (111) surface . The BMR probes a three-fold out-of-plane spin texture, in addition to an in-plane one at the STO(111) surface 2DEG. These findings open a new branch in spintronics, which discusses the nonlinear transport effects in spin-polarized nonmagnetic materials, and is therefore referred to as nonlinear spintronics, applicable to frequency doubling  and energy harvesting applications .
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