Temporal Evolution of Low-Temperature Phonon Sidebands in Transition Metal Dichalcogenides
Roberto Rosati, Koloman Wagner, Samuel Brem, Raül Perea‐Causín, Edith Wietek, Jonas Zipfel, Jonas D. Ziegler, Malte Selig, Takashi Taniguchi, Kenji Watanabe, Andreas Knorr, Alexey Chernikov, Ermin Malić
Abstract
Low-temperature photoluminescence (PL) of hBN-encapsulated monolayer tungsten diselenide (WSe2) shows a multitude of sharp emission peaks below the bright exciton. Some of them have been recently identified as phonon sidebands of momentum-dark states. However, the exciton dynamics behind the emergence of these sidebands has not been revealed yet. In this joint theory–experiment study, we theoretically predict and experimentally observe time-resolved PL, providing microscopic insights into the thermalization of hot excitons formed after optical excitation. In very good agreement between theory and experiment, we demonstrate a spectral red-shift of phonon sidebands on a time scale of tens of picoseconds, reflecting the phonon-driven thermalization of hot excitons in momentum-dark states. Furthermore, we predict the emergence of a transient phonon sideband that vanishes in the stationary PL. The obtained microscopic insights are applicable to a broad class of 2D materials with multiple exciton valleys.