Photon wavelength dependent valley photocurrent in multilayer MoS2

Abstract

The degree of freedom (DOF) of the $K$ (${K}^{\ensuremath{'}}$) valley in transition-metal dichalcogenides, especially molybdenum disulfide (${\mathrm{MoS}}_{2}$), offers an opportunity for next-generation valleytronics devices. In this work, the $K$ (${K}^{\ensuremath{'}}$) valley DOF of multilayer ${\mathrm{MoS}}_{2}$ is studied by means of the photon wavelength dependent circular photogalvanic effect (CPGE) at room temperature upon a strong external out-of-plane electric field induced by an ionic liquid (IL) gate, which breaks the spatial-inversion symmetry. It is demonstrated that only on resonant excitations in the $K$ (${K}^{\ensuremath{'}}$) valley can the valley-related CPGE signals in multilayer ${\mathrm{MoS}}_{2}$ with an IL gate be detected, indicating that the valley contrast is indeed regenerated between the $K$ and ${K}^{\ensuremath{'}}$ valleys when the electric field is applied. As expected, it can also be seen that the $K$ (${K}^{\ensuremath{'}}$) valley DOF in multilayer ${\mathrm{MoS}}_{2}$ can be modulated by the external electric field. The observation of photon wavelength dependent valley photocurrent in multilayer ${\mathrm{MoS}}_{2}$, with the help of better Ohmic contacts, may pave a way for optoelectronic applications of valleytronics in the future.