title: Giant magneto-optical Kerr effect and universal Faraday effect in thin-film topological insulators.
abstract: Topological insulators can exhibit strong magneto-electric effects when their time-reversal symmetry is broken. In this Letter we consider the magneto-optical Kerr and Faraday effects of a topological insulator thin film weakly exchange coupled to a ferromagnet. We find that its Faraday rotation has a universal value at low frequencies θF=tan(-1)α, where α is the vacuum fine structure constant, and that it has a giant Kerr rotation θK=π/2. These properties follow from a delicate interplay between thin-film cavity confinement and the surface Hall conductivity of a topological insulator's helical quasiparticles.
authors.affiliation: Department of Physics, University of Texas, Austin, Texas 78712, USA.
authors.forename: Wang-Kong
authors.initials: WK
authors.lastname: Tse
authors.forename: A H
authors.initials: AH
authors.lastname: MacDonald