Valley and Spin Resolved Photocurrent in Atomically Thin MoS₂

The ability to access the coupled valley-spin indexes in transition metal dichalcogenide monolayers is one of the most intriguing features of these 2D semiconductors. Control and manipulation of the valley properties have been recently been achieved, but these approaches rely mostly on optical measurements and sensing. Here we demonstrate a new method for electrical readout of optically generated valley polarization based on breaking the valley degeneracy with an out-of-plane magnetic field B_z. At the same time, we detect the spin alignment of carriers electrically using the established approach of spin-sensitive ferromagnetic contacts. In our experiments, the presence of B_z is found to induce a significant modulation in the photocurrent from monolayer MoS₂ as a function of the handedness of the circularly polarized excitation. We attribute this effect to the unbalanced transport of valley polarized trions, which experience opposite Zeeman shifts in the K and K’ valleys. Our interpretation is further supported by a comparison to the behavior in samples of the 2H bilayer MoS₂, with its higher symmetry. The efficient tuning and detection of the valley-polarized photocurrent opens up new directions to develop optoelectronic devices making use of the valley degree of freedom.