Intrinsic contribution to nonlinear thermoelectric effects in topological insulators

Irradiation of strong light on a material leads to numerous nonlinear effects that are essential to understand the physics of excited states of the system and optoelectronics. Here, we study the nonlinear thermoelectric effects due to the electric and thermal fields applied on a noncentrosymmetric system. The phenomenon arises on the Fermi surface with the transitions of electrons from the valence to conduction bands. We derive the formalism to investigate these effects and find that the nonlinearity in these effects, namely, nonlinear Seebeck and nonlinear Peltier effects, depends on the ratio of the nonlinear to linear conductivities. The theory is tested for a hexagonally warped and gapped topological insulator. Results show enhancement in the longitudinal and Hall effects on increasing the warping strength but show opposite behavior with the surface gap.