Valley Hall transport of photon-dressed quasiparticles in two-dimensional Dirac semiconductors

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 ofboth 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 delta(eta) (eta is the valley index) that strongly depend on field amplitude and polarization. Nonequilibrium carrier distribution functions are determined by the pump field frequency omega as well as the ratio of intraband relaxation time tau and interband recombination time tau(rec). We obtain analytic results in three regimes, when (I) all relaxation processes are negligible, (II) tau << tau(rec),( )and (III) tau >> tau(rec), and display corresponding asymptotic dependences on delta(eta) and omega. 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.