Abstract
We present a theory of the photovoltaic valley-dependent Hall effect in a two-dimensional (2D) Dirac semiconductor subject to an intense near-resonant electromagnetic field. Our theory captures and elucidates the influence of both the field-induced resonant interband transitions and the nonequilibrium carrier kinetics on the resulting valley Hall transport in terms of photon-dressed quasiparticles (PDQs). The non-perturbative renormalization effect of the pump field manifests itself in the dynamics of the PDQs, with a quasienergy spectrum characterized by dynamical gaps δη (η is the valley index) that strongly depend on field amplitude and polarization. Nonequilibrium carrier distribution functions are determined by the pump field frequency ω as well as the ratio of intraband relaxation time τ and interband recombination time τrec. We obtain analytic results in three regimes, when (I) all relaxation processes are negligible, (II) τ ≪ τrec, and (III) τ ≫ τrec, and display corresponding asymptotic dependences on δη and ω. We then apply our theory to 2D transition-metal dichalcogenides, and find a strong enhancement of valley-dependent Hall conductivity as the pump field frequency approaches the transition energies between the pair of spin-resolved conduction and valence bands at the two valleys.
Highlights
Low-dimensional quantum systems subject to an externally applied large power high frequency electromagnetic field (EMF) display a great variety of interesting phenomena, such as multi-photon induced macroscopic quantum tunneling [1], multi-photon Rabi oscillations and the dynamic Stark effect in superconducting or hybrid qubits [2, 3], dissipationless electron transport [4], polaritons and condensates [5, 6], and Floquet nonequilibrium states [7, 8]
The non-perturbative renormalization effect of the pump field manifests itself in the dynamics of the photon-dressed quasiparticles, with a quasienergy spectrum characterized by dynamical gaps δη (η is the valley index) that strongly depend on field amplitude and polarization
The quasienergy spectrum of such photon-dressed quasiparticles (PDQs) shows a dynamical gap [10, 11] that is proportional to the amplitude of the EMF, and the nonequilibrium steady state of the PDQs is determined by interplay between different time scales: the inverse dynamical gap, inverse frequency, and relaxation times [12]
Summary
Low-dimensional quantum systems subject to an externally applied large power high frequency electromagnetic field (EMF) display a great variety of interesting phenomena, such as multi-photon induced macroscopic quantum tunneling [1], multi-photon Rabi oscillations and the dynamic Stark effect in superconducting or hybrid qubits [2, 3], dissipationless electron transport [4], polaritons and condensates [5, 6], and Floquet nonequilibrium states [7, 8]. In many cases of interest, the quantum dynamics of systems strongly interacting with an EMF can be described in terms of nonequilibrium quasiparticles called photon-dressed quasiparticles (PDQs) [2, 9]. They are characterized by a specific quasienergy spectrum and nonequilibrium steady-state distribution functions. Such a quasiparticle description is useful for nearresonant excitation, i.e. when the frequency of the EMF is close to the difference of the intrinsic energy levels. While the linear-response optical conductivity of TMDs has been extensively studied in a number of works (e.g., Refs. [28,29,30]), nonlinear optical phenomena [31] remain largely unexplored despite attracting increasing attention [32, 33]
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