Spin/valley dynamics of resident electrons and holes in gated monolayer WSe$_{\mathrm{2}}$

Robust spin-valley coupling is a key prerequisite for next generation spintronic and valleytronic devices. Monolayer transition metal dichalcogenides provide an excellent platform to explore the spin-valley physics of electrons, holes and excitons. In contrast to the short (picosecond) recombination lifetimes of excitons and trions, recent studies of electron-doped MoS$_{\mathrm{2}}$ and WS$_{\mathrm{2}}$ monolayers demonstrated surprisingly long (nanosecond) spin lifetimes and spin coherence of resident electrons [1,2]. Here we use continuous wave (CW) and time-resolved Kerr rotation spectroscopy (TRKR) to explore the spin and valley polarization dynamics in electrostatically-gated crystals of exfoliated monolayer WSe$_{\mathrm{2}}$. Long-lived polarization dynamics of both resident electrons and holes are observed. Measurements as a function of applied magnetic field, temperature, and carrier doping density will be presented. [1] Yang \textit{et al.}, \textit{Nature Phys. }\textbf{11}, 830 (2015). [2] Yang \textit{et al.}, \textit{Nano Lett. }\textbf{15}, 8250 (2015).