Observation of Layer Dependent Ultrafast Carrier dynamics and Interlayer Coherent Phonon Dynamics in PdSe2 Films

In this work, by employing ultrafast optical pump-probe spectroscopy, we investigated the photocarrier dynamics as well as the thickness dependent interlayer coherent phonon modes in PdSe2 films. Two low-frequency phonon modes in PdSe2 films are identified after photoexcitation at 780 nm. The higher frequency mode is ascribed to the interlayer breathing mode, and the lower one is assigned to the standing wave mode, and the frequency variation and the related parameters (interlayer force constant and sound velocity) of the two modes are investigated.