Visualization of lattice dynamics and atomic motion in WSe_2 monolayer

Atomically-thin materials have drawn great interest due to their exotic properties leading to a variety of promising new applications. However, the out-of-equilibrium dynamics of these materials are still not fully understood. Ultrafast electron diffraction (UED) is a powerful technique for the investigation of the transient structural dynamics of monolayers with unprecedented spatiotemporal resolution. The UED results of WSe2_ monolayers are reported and the suppression of the intensity of the Bragg diffraction spots following laser excitation is attributed to electron-phonon and phonon-phonon scattering. A two-temperature model is used to accurately describe these dynamics due to the low thermal conduction of the monolayer. Furthermore, the reported lifetimes are fit using a single-mode relaxation time approximation.