Terahertz signatures of ultrafast Dirac fermion relaxation at the surface of topological insulatorsстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 15 декабря 2021 г.
Аннотация:Topologically protected surface states present rich physics and promising spintronic, optoelectronic, and photonic applications thatrequire a proper understanding of their ultrafast carrier dynamics. Here, we investigate these dynamics in topological insulators (TIs)of the bismuth and antimony chalcogenide family, where we isolate the response of Dirac fermions at the surface from theresponse of bulk carriers by combining photoexcitation with below-bandgap terahertz (THz) photons and TI samples with varyingFermi level, including one sample with the Fermi level located within the bandgap. We identify distinctly faster relaxation of chargecarriers in the topologically protected Dirac surface states (few hundred femtoseconds), compared to bulk carriers (fewpicoseconds). In agreement with such fast cooling dynamics, we observe THz harmonic generation without any saturation effectsfor increasing incident fields, unlike graphene which exhibits strong saturation. This opens up promising avenues for increased THznonlinear conversion efficiencies, and high-bandwidth optoelectronic and spintronic information and communication applications.