Unveiling surface and bulk contributions in temperature dependent THz emission from Bi2Te3

Abstract

We report evolution of the pulsed terahertz (THz) emission from Bi2Te3 topological insulator in a wide temperature range, where an interplay between the surface and bulk contributions can be addressed in a distinguishable manner. A circular photogalvanic effect-induced surface current contribution to THz generation can be clearly identified in the signal, otherwise, overwhelmed by the hot carrier decoherence in the bulk states. With the decreasing temperature, an initial sharp increase in the surface THz signal is observed before it attains a constant value below ~200 K. The bulk-to-surface scattering channels via carrier-phonon scattering are dominant only above the bulk-Debye temperature of ~180 K, and the temperature-independent behavior of it at lower temperatures is indicative of robust nature of topological surface states. THz emission due to ultrafast photon drag current in the bulk states is almost independent of temperature in the entire range, while the combined photo-Dember and band-bending effects induced photocurrent is doubled at 10 K.