Light-field and spin-orbit-driven currents in van der Waals materials

Abstract

<jats:title>Abstract</jats:title><jats:p>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.</jats:p>

Time-Domain Investigations of Coherent Phonons in van der Waals Thin Films

“…Due to the strong electron–electron interaction in vdW layers, pulsed excitation can yield original configurations for the photocarriers, such as relatively long-lived hot electron distribution, excitonic quasiparticles, plasmons, phonon-polaritons [ 200 , 209 ], etc. A comprehensive experimental and theoretical knowledge on these exotic physical behaviors upon pulsed optical excitation is well established, with even advanced schemes for coherent control of specific features as discussed in Section 4.1 [ 206 , 207 , 208 ]. Electron–phonon interaction can be strongly modified by the environment, especially in vdW heterostructures, with the introduction of prominent couplings to remote phonons [ 61 , 216 , 217 , 222 ].…”

“…Different aspects from the build-up of the excitonic quasiparticles [ 201 , 202 ], to their subsequent diffusion [ 203 ], Auger interaction, and other recombination mechanisms [ 204 , 205 ], have been resolved through all-optical time-domain studies. In addition to photocarrier incoherent population, the ultrafast coherent dynamics of specific features (valley in the Brillouin zone, spin…) can be followed, and controlled, using advanced schemes [ 206 , 207 , 208 ]. Another peculiar case is the one of graphene.…”

“…. ) can be followed, and controlled, using advanced schemes [206][207][208]. Another peculiar case is the one of graphene.…”

Berry curvature-induced local spin polarisation in gated graphene/WTe$_2$ heterostructures

“…Besides complementing electrical detection schemes for in-plane spins toward probing out-of-plane spins in such heterostructures, they reveal the gate-dependent spatial distribution of the current-induced spin polarisation. Considering observed spin diffusion lengths on the order of 10 µm in bare graphene [2] and 2 µm in MoTe 2 [33], far-field optical probes can indeed access relevant length scales via local and non-local optoelectronic readout schemes [26,34]. Furthermore, the presented generic model, merging classical diffusion theory with topology, should be applicable also to other 2D materials and their heterostructures where Berry curvature plays a crucial role, such as transition metal dichalcogenides or nodal line semimetals [23].…”

“…This establishes a relationship between Kerr microscopy, spintronics, topological band theory, and nonreciprocal transport coefficients [18][19][20], which also determine the non-linear anomalous Hall effect [21][22][23] and photocurrents in topological metals [24][25][26]. While the current-induced anomalous Hall response in the bulk of either graphene or WTe 2 vanishes due to crystalline symmetries, we here exploit the reduced interface symmetry of graphene/WTe 2 heterostructures to achieve a controllable net spin-charge interconversion.…”