Spin Edelstein effect in irradiated topological insulator thin films

We investigate the low-temperature spin Edelstein effect in topological insulator thin films subjected to circularly polarized light. Using a high-frequency Floquet formalism, we derive an effective Hamiltonian that captures light-induced renormalization of the mass gap and Fermi velocity. Based on this model, we compute the spin Edelstein susceptibilities using the Kubo linear-response theory, accounting for both intraband and interband contributions. Our results reveal that optical driving enables strong tunability of spin polarization, with critical behavior emerging at the Floquet-engineered band structure where the effective Fermi velocity vanishes. We further demonstrate that surface asymmetry, hybridization strength, and interband relaxation processes play crucial roles in shaping the spin responses. These findings suggest promising routes for dynamically controlling spin accumulation in topological materials via light, offering new opportunities for spintronic applications.