Topological insulator materials for advanced nonlinear in-chip plasmonic devices

Topological insulator (TIs) has fascinating nonlinear optical properties that are inaccessible in classical materials. We report extraordinarily large third harmonic generation (THG) signal from telecom wavelength incidences in Bi₂Se₃ and Sb₂Te₃ grown by molecular beam epitaxy (MBE). Nonlinear optical measurements performed in samples with different thicknesses and stoichiometries are combined with angle-resolved photoemission spectroscopy (ARPES) characterizations to elucidate the nature of the giant THG signals. Moreover, by integrating with nanoscaled plasmonic devices on top of TIs, the strong plasmonic field enhancement further enables us to produce controllable nonlinear optical functionalities with very low input energy threshold. Our findings demonstrate a great potential for a new class of topological materials based on-chip nonlinear photonic devices.