Microwave spectroscopy of three-dimensional topological insulators

    Topological insulators (TI) belong to the phase category which goes beyond the theory of spontaneous symmetry breaking, well describing the classical phases. TI were initially theoretically predicted for materials with strong spin-orbit interactions that lead to the reversal of the sequence of the valence band and the conduction band. Consequently, these materials behave as insulators in the volume while their surfaces host metallic states. The metallic states have an unusual spin structure, with the electron spin locked to its momentum, described by the Dirac-type Hamiltonian. These states are protected by the time reversal symmetry, thus they are resistant to non-magnetic disturbances.
    In the seminar, I will present the application of microwave spectroscopy (using a standard electron paramagnetic resonance spectrometer) to studies of three-dimensional topological insulators. The technique allows measurements of both resonant (electron spin resonances, ferromagnetic resonances, cyclotron resonances) and non-resonant effects (Shubnikov-de Haas oscillations, weak localization and antilocalization). I will refer our earlier results on Bi2Te3 and Bi2Se3 as well as some new data on the three-dimensional TI doped with magnetic ions.