Transitional Faraday and Kerr effect in hybridized topological insulator thin films

Abstract

We theoretically investigate quantum phase transitions from topologically non-trivial to trivial states in three-dimensional hybridized topological insulator (TI) ultra-thin films. The interplay between the hybridization of the top and bottom surface states (SSs) and Zeeman energy gives rise to topological and normal insulating phases. By tuning the Zeeman energy, we can drive phase transition between these two phases by closing and reopening the band gap. Furthermore, we impinge a Gaussian beam on the surface of the 3D TI to study the Faraday rotation (FR) and magneto-optical Kerr effect (MOKE) in the presence of an external magnetic field, while explicitly taking into account the hybridization between the top and bottom Dirac SSs of the TI film. The FR and MOKE change sign when the polarization is changed from s to p. We demonstrate that giant FR and MOKE can be achieved by tuning the external magnetic field. Furthermore, the MOKE signal takes a sharp anti-phase peak at the charge neutrality point as the system goes from the quantum spin Hall insulator (QSHI) to the semimetallic state. Lastly, the MOKE and FR in the bottom and top SSs can be independently tuned for intra-band and inter-band transitions via n-type and p-type doping respectively.