Highly tunable spin-polarized nonlinear Nernst effect.

The controllable generation of spin polarization is essential for spintronics, for which 3D topological insulators (TIs) are ideal candidate materials because of the fascinating spin-momentum locking of their topological surface states (TSSs). Here, we propose a band tilt-induced nonlinear Nernst effect (NLNE) in 3D TIs in the absence of magnetic field. It's found that the presence of finite band tilt can induce the imbalance of two spin carriers and give rise to spin-polarized NLNE current. Remarkably, we show that, the realized carrier spin polarization exhibits highly flexible tuning regimes i.e. rapid and smooth tuning regimes, and near-unity spin polarization can be generated within a wide range of tunable parameters. The spin-polarized NLNE proposed here is also robust against temperature, thus providing an alternative mechanism to realize room-temperature high-degree spin polarization.