Photogalvanic effect induced by intervalley relaxation in a strained two-dimensional Dirac monolayer

We theoretically study the photogalvanic effect in a strained two-dimensional transition-metal dichalcogenide monolayer due to deformation-induced lowering of the monolayer symmetry and electron-density difference in opposite valleys. This effect arises as a system response to a scalar nonequilibrium perturbation (electron-density difference in the valleys), which is in contrast with the conventional photogalvanic effect, represents the second-order response to an external electromagnetic radiation. Using the description of linear and nonlinear interband recombination, we develop a theory for a p-type and an intrinsic monolayer semiconductor. We show that at low temperatures, the photogalvanic current is caused by the impurity relaxation processes controlling the valley population imbalance.