Enhanced room-temperature spin-valley coupling in V-doped MoS2

Abstract

Achieving room-temperature valley polarization in two-dimensional (2D) atomic layers (2D materials) by substitutional doping opens new avenues of applications. Here, monolayer ${\mathrm{MoS}}_{2}$, when doped with vanadium at low (0.1 atomic %) concentrations, is shown to exhibit high spin-valley coupling, and hence a high degree of valley polarization at room-temperature. The atomic layers of ${\mathrm{MoS}}_{2}$ (MS) and V-doped ${\mathrm{MoS}}_{2}$ (VMS) are grown via the chemical vapor deposition-assisted method. The formation of new energy states near the valence band is confirmed from band gap calculations and also from the density functional theory--based band structure analyses. Time-reversal symmetry broken energy shift in the equivalent valleys is predicted in VMS, and the room-temperature chirality-controlled photoluminescent (PL) excitation measurements indicate such a shift in valley exciton energies (\ensuremath{\sim}35 meV). An enhanced valley polarization in VMS (\ensuremath{\sim}42%) is observed in comparison to that in MS (12%), while in MS, the chirality-controlled excitations did not show the difference in emission energies. Spin Hall effect of light--based optical rotation measurements indicate the asymmetric absorption among the two different chiralities of the incident light, hence supporting the existence of room-temperature valley polarization. This study opens possibilities of room-temperature opto-spintronics using stable 2D materials.