Propagating Dirac plasmon polaritons in topological insulators

We investigate the excitation of propagating Dirac plasmon polaritons (DPPs) in topological insulator (TI) thin films. A series of TI thin films were grown by molecular beam epitaxy. Periodic gold grating couplers with different periodicity were fabricated on the TI films to excite the propagating DPPs. A series of absorption peaks that shift with the grating periodicity were observed in Fourier transform infrared spectroscopy transmission scans. We have ruled out any source other than the excitation of propagating DPPs that could have caused the peaks to appear. The peak dispersion is consistent with theoretical predictions for coupled DPPs in TI thin films.