Anomalous Oscillating Behavior of Ultrafast Spatiotemporal Hot Carrier Diffusion in Two-Dimensional PtSe2

Abstract

Ultrafast spatiotemporal responses to laser pulses are important forunderstanding fundamental processes in solids, such as diffusion of carriers andcoherent vibrations of lattices. Here, we present anomalous spatiotemporaldynamics in atomically thin PtSe2, a new rising two-dimensional material inelectronics and optoelectronics. We utilize transient absorption scanningmicroscopy to investigate the carrier diffusion dynamics. Interestingly, theobserved spatial width of the optical response shows oscillations with picosecondperiods, in contrast to ordinary systems in which the spatial distributionmonotonically broadens with time. Wefind that this anomalous oscillatingbehavior arises from the dynamic superposition between the hot carrier diffusion and coherent layer-breathing lattice vibrations.Further, we obtain the thickness-dependent diffusivities of hot/cooled carriers and carrier cooling time constants, which are criticalfactors for designing 2D PtSe2-based ultrafast devices. This work provides novel observation and understanding of ultrafastspatiotemporal hot carrier dynamics and its interplay with coherent phonons.