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 secondorder 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.