Time-Domain THz studies of topological insulator waveguides

Topological insulators (TI) subject to time-reversal symmetry breaking perturbations are well known to exhibit quantized magneto-elecric effect. In conventional transmission experiments, light being transmitted through such TI's will experience Faraday and Kerr rotations of polarization. However, these effects are on the order of fine structure constant α which makes it challenging to observe experimentally. In this work, we utilize TI's at the interface between guiding and cladding layers of a parallel-plate waveguide to induce coupling between guided TE and TM modes. It was previously predicted that this coupling is dependent on the number of filled Landau levels in the TI surface plus an axionic term that is measure of the topological invariant. Here we present the working principle of the waveguide device and provide experimental results of time-domain terahertz (THz) spectroscopy studies on it.