Carrier and Phonon Dynamics in Multilayer WSe₂ Captured by Extreme Ultraviolet Transient Absorption Spectroscopy

Carrier and phonon dynamics in a multilayer WSe₂ film are captured by extreme ultraviolet (XUV) transient absorption (TA) spectroscopy at the W N_6,7, W O_2,3, and Se M_4,5 edges (30-60 eV). After the broadband optical pump pulse, the XUV probe directly reports on occupations of optically excited holes and phonon-induced band renormalizations. When compared with density functional theory calculations, XUV transient absorption due to holes is identified below the W O₃ edge whereas signals at the Se M_4,5 edges are dominated by phonon dynamics. Therein, 0.4 ps hole relaxation time, 1.5 ps carrier recombination time, and 1.7 ps phonon heating time are extracted. The acquisition of hole and phonon-induced signals in a single experiment can facilitate the investigation of the correlations between electron and phonon dynamics. Furthermore, the simultaneous observation of signals from different elements can be further extended to explore photochemical processes in multilayers and alloys, thereby providing key information for their applications in electronics, photocatalysts, and spintronics.