Spatial-temporal imaging electronic dynamics in few-layer graphene

Abstract

Abstract Revealing the ultrafast carrier dynamics with spatial, energy and time resolution is critical for achieving a comprehensive understanding of the ultrafast electronic dynamics of two-dimensional materials and heterostructures. Here, by time-resolved photoemission electron microscopy (Tr-PEEM) measurements, we reveal the layer-dependent ultrafast electronic dynamics of monolayer (1 ML), bilayer (2 ML), 4 ML graphene as well as bulk graphite. In contrast to 2 ML and thicker graphene, photo-excited electrons in 1 ML graphene relax much faster, which is attributed to the unique massless linear Dirac cone dispersion, allowing electrons to relax by continuously emitting phonons. Moreover, transient photoelectron redistribution shows an energy shift between 1 ML and 2 ML graphene, highlighting the critical role of the bandgap in 2 ML graphene on the carrier relaxation dynamics. Our work demonstrates the power of Tr-PEEM in revealing the ultrafast dynamics of two-dimensional materials and heterostructures with spatial-temporal information, and provides information for the layer-dependent ultrafast relaxation dynamics in few-layer graphene.