Valley mediated singlet- and triplet-polaron dynamics in a doped WSe₂ monolayer

The valley degree of freedom, as an additional quantum index in the electronic bands of solids, has found an increasingly important role in understanding the electronic and optical properties of atomically thin materials. Here, we study the formation of new optical resonances in a WSe2 monolayer as the doping level gradually increases. Singlet and triplet polarons are new quasiparticles that arise when optically excited electron-hole pairs couple to the Fermi sea in the same or opposite valleys. Using two-dimensional electronic coherent spectroscopy, we reveal their distinct quantum dephasing, valley depolarization, and tunable valley coherence.