Optical activation of nonlinear Hall effect in topological insulators with warped Fermi surface

RESUMO

Topological insulators (TIs) with hexagonally warped Fermi surface are natural platforms for the nonlinear Hall effect, as warping breaks inversion symmetry while preserving time-reversal symmetry (TRS). Here we show that this inversion breaking alone is insufficient: although warping generates a strongly anisotropic Berry curvature, the preserved threefold rotational symmetry forces the equilibrium Berry curvature dipole (BCD) to vanish identically. We demonstrate that linearly polarized light removes this symmetry obstruction: in the off-resonant Floquet regime, it lowers the rotational symmetry while preserving TRS, thereby generating a finite BCD whose magnitude, orientation, and sign are continuously tunable by the light intensity and polarization. For realistic Bi$_2$Te$_3$ parameters, we show that the induced BCD reaches $\sim$0.03~nm, yielding microampere-scale nonlinear Hall currents under experimentally accessible conditions. Our results therefore establish Floquet symmetry engineering as a route to activating the symmetry-forbidden nonlinear transport on TI surfaces without breaking the TRS.