Magneto-optical conductivity and giant Faraday-Kerr rotation in Floquet topological insulators

We study the surface state-dependent magneto-optical properties of an ultrathin Floquet topological insulator (FTI) under influence external perpendicular magnetic field in terahertz frequency regime. Under picture, we treat circularly polarized off-resonant light as perturbation that introduces a mass gap at Dirac cone, thus, making state fermions massive. By tuning optical energy FTI thin-film system, various electronic phase transitions can be driven between trivial and band state. Using Kubo formalism, derive real imaginary parts longitudinal Hall conductivities demonstrate these are sensitively influenced by strength field, chemical potentials. On other hand, insulators exhibit strong magneto-optic effects. further compute Kerr Faraday rotation angles show giant rotations achieved thin film knobs, such fields. The symmetric (top) antisymmetric (bottom) states controlled for interband intraband via gate bias voltage. Our results reveal intriguing versatile system whose effectively tuned optically, magnetically electrically, uncovering photonics optoelectronics device application potentials FTI.