Abstract
Abstract This review aims to provide an overview over recent developments of light-driven currents with a focus on their application to layered van der Waals materials. In topological and spin-orbit dominated van der Waals materials helicity-driven and light-field-driven currents are relevant for nanophotonic applications from ultrafast detectors to on-chip current generators. The photon helicity allows addressing chiral and non-trivial surface states in topological systems, but also the valley degree of freedom in two-dimensional van der Waals materials. The underlying spin-orbit interactions break the spatiotemporal electrodynamic symmetries, such that directed currents can emerge after an ultrafast laser excitation. Equally, the light-field of few-cycle optical pulses can coherently drive the transport of charge carriers with sub-cycle precision by generating strong and directed electric fields on the atomic scale. Ultrafast light-driven currents may open up novel perspectives at the interface between photonics and ultrafast electronics.
Highlights
In the past decade, layered van der Waals materials have regained significant interest because of their emergent optoelectronic properties when reduced to two-dimensional (2D) layers [1, 2]
After a pulsed photoexcitation, the presence of a large density of charge carriers can alter the Coulomb screening in monolayer transition metal dichalcogenides (TMDs) [22,23,24,25,26,27,28,29], such that both the quasi-particle band gap and the excitonic binding energies are renormalized on femtosecond time scales
In topological insulator thin films, the charge carrier dynamics after optical excitation are governed by a hot electron ensemble [63], in stark contrast to the excitonic response of TMDs
Summary
In the past decade, layered van der Waals materials have regained significant interest because of their emergent. In topological insulator thin films, the charge carrier dynamics after optical excitation are governed by a hot electron ensemble [63], in stark contrast to the excitonic response of TMDs. The spin and momentum depolarization have been shown to take place on a common sub-picosecond time scale as expected for spin-momentum locked surface states [60, 64, 65]. We present selected examples for helicity-driven currents in van der Waals materials, including TMDs with their coupling of valley and out-of-plane spin, topological insulators with their in-plane spin-momentum locking, and Weyl semimetals with their chiral electron states. In the last section of the review, we illustrate how strong and ultrafast light-fields are employed to directly drive currents at optical frequencies (Section 4), and how such light-fielddriven currents could be integrated into terahertz (THz) circuits for generation high-speed optoelectronics (Section 5)
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