Influence of Spin-Valley Coupling on Photogalvanic Photocurrents in Layered Transition Metal Dichalcogenides

Monolayer semiconducting transition metal dichalcogenides (TMDs) have been studied theoretically; they were expected to exhibit electric field- and magnetic field-dependent robust valley-selective interactions, which have been observed even at room temperature. Their direct band gap at monolayers offers a unique characteristic of coupling with spin degree of freedom, resulting in valley contrast and polarization, as observed in photoluminescence [4, 5]. In addition to the strong SOC, their lattice structure, existence or absence of centrosymmetry, and stacking play a crucial role in valley-dependent properties. For this reason, photogalvanic photocurrents could offer highly efficient valleytronic device functionalities. In this chapter, we will first introduce the basic information about TMDs, such as lattice structure, symmetry, and stacking order, particularly in respect to photogalvanic effect—PGE. The phenomenology described for graphene in Chaps.  2 and 3 is also applicable to monolayer TMDs, except a few differences. However, the microscopic origin is distinct due to the spin-valley coupling. Here, the outcome of this coupling together with optical selection rules will be discussed. Finally, the expectation and influence of spin-valley coupling in photocurrent contributions nonlinear-in-electric field due to second-order response will be given with light impinging geometries.