A hexagonal warping term has been proposed recently to explain the experimentally observed 2D equal energy contours of the surface states of the topological insulator Bi2Te3. Differing from the Dirac fermion Hamiltonian, the hexagonal warping term leads to the opening up of a band gap by an in-plane magnetization. We study the transmission between two Bi2Te3 segments subjected to different in-plane magnetizations and potentials. The opening up of a bandgap, and the accompanying displacement and distortion of the constant energy surfaces from their usual circular shapes by the in-plane magnetizations, modify the transverse momentum overlap between the two Bi2Te3 segments, and strongly modulate the transmission profile. The strong dependence of the TI surface state transport of Bi2Te3 on the magnetization orientation of an adjacent ferromagnetic layer may potentially be utilized in, e.g., a memory readout application.

Plane polarized electromagnetic waves propagating through a dielectric medium parallel to a magnetic field undergo Faraday rotation (FR) of their polarization. “Giant” Faraday rotation by as much as 0.1 rad was recently observed for terahertz waves with graphene over a SiC substrate. We show that for the (more technologically useful) optical frequency range, the same effect may be achieved with interband transitions between Landau levels formed by application of real or pseudo-magnetic fields induced by strain. At some resonant condition, the FR angle shows a sharp transition and sign reversal, which may be used to rotate the polarizations of the sodium doublet D-lines so as to be perpendicular to each other.