Terahertz signatures of ultrafast Dirac fermion relaxation at the surface of topological insulators at room temperature

Abstract

Topologically-protected surface states present rich physics and promising spintronic, optoelectronic and photonic applications that require 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 the response of bulk carriers by combining photoexcitation with below-bandgap terahertz (THz) photons with TI samples with varying Fermi level, including one sample with the Fermi level located within the bandgap. We identify distinctly faster relaxation of charge carriers in the topologically-protected Dirac surface states (few hundred femtoseconds), compared to bulk carriers (few picoseconds). In agreement with such fast cooling dynamics, we observe THz harmonic generation without any saturation effects for increasing incident fields, unlike graphene which exhibits strong saturation. This opens up promising avenues for increased THz nonlinear conversion efficiencies, and high-bandwidth optoelectronic and spintronic information and communication applications.

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Cited by in corpus (8)

• Milliwatt terahertz harmonic generation from topological insulator metamaterials
• Tunable room temperature nonlinear Hall effect from the surfaces of elementary bismuth thin films
• Observation of terahertz second harmonic generation from Dirac surface states in the topological insulator Bi${}_2$Se${}_3$
• Terahertz third-harmonic generation of lightwave driven Weyl fermions far from equilibrium
• Ultrafast electron dynamics in a topological surface state observed in two-dimensional momentum space
• Terahertz harmonic generation across the Mott insulator-metal transition
• Ultrafast electronic heat dissipation through surface-to-bulk Coulomb coupling in quantum materials
• Research on topological materials using ultrafast spectroscopy