Surface State-Dominated Photoconduction and THz Generation in Topological BiTeSe Nanowires.

Topological insulators constitute a fascinating class of quantum materials with nontrivial, gapless states on the surface and insulating bulk states. By revealing the optoelectronic dynamics in the whole range from femto- to microseconds, we demonstrate that the long surface lifetime of BiTeSe nanowires allows us to access the surface states by a pulsed photoconduction scheme and that there is a prevailing bolometric response of the surface states. The interplay of the surface and bulk states dynamics on the different time scales gives rise to a surprising physical property of BiTeSe nanowires: their pulsed photoconductance changes polarity as a function of laser power. Moreover, we show that single BiTeSe nanowires can be used as THz generators for on-chip high-frequency circuits at room temperature. Our results open the avenue for single BiTeSe nanowires as active modules in optoelectronic high-frequency and THz circuits.