Nonequilibrium carrier dynamics and band structure of graphene on two-dimensional tin

Intercalation of epitaxial graphene on SiC(0001) with Sn results in a well-ordered Sn $(1\ifmmode\times\else\texttimes\fi{}1)$ structure on the SiC surface with quasifreestanding graphene on top. While the electronic properties of the individual layers have been studied in the past, emerging phenomena arising from possible interlayer interactions between the 2D Sn layer and graphene remain unexplored. We use time- and angle-resolved photoemission spectroscopy to reveal a surprisingly short-lived nonequilibrium carrier distribution inside the Dirac cone of Sn-intercalated graphene. Further, we find that the graphene $\ensuremath{\pi}$ band exhibits a transient increase in binding energy that we attribute to charging of the graphene layer with holes. We interpret our results with support from density functional theory calculations of the graphene 2D Sn heterostructure that reveal a substantial hybridization between the graphene $\ensuremath{\pi}$ bands and Sn states, providing a channel for efficient ultrafast charge transfer between the layers. Our results on the graphene 2D Sn model system are expected to trigger similar investigations on related heterostructures obtained by intercalation of epitaxial graphene. Regarding the huge choice of materials that have been successfully intercalated in the past, we believe that the interlayer interactions revealed in the present paper only represent the tip of the iceberg, with many fascinating emerging phenomena to be discovered in the near future.