Charge transfer between van der Waals coupled metallic 2D layers

TL;DR

This study investigates charge transfer in a layered heterostructure of potassium, graphene, and lead on SiC, revealing significant electron donation from potassium to both graphene and lead layers, with a notable distribution of transferred electrons.

Contribution

It provides detailed experimental insights into charge transfer mechanisms in multi-layered 2D heterostructures using synchrotron-based photoemission spectroscopy.

Findings

Approximately 44% of K-donated electrons transfer to Pb layer.

About 56% of electrons remain in the graphene layer.

K adsorption causes significant n-doping in graphene and electron transfer to Pb.

Abstract

Van der Waals heterostructures have become a rapidly growing field in condensed matter research, offering a platform to engineer novel quantum systems by stacking different two-dimensional (2D) materials. A diverse range of material combinations, including hexagonal boron nitride, transition metal dichalcogenides and graphene, with electronic properties spanning from insulating to semiconducting, metallic, and semimetallic, have been explored to tune the properties of these heterostacks. However, understanding the interactions and charge transfer between the stacked layers remains challenging, particularly when more than two layers are involved. In this study, we investigate the charge transfer in a potassium-adlayer/graphene/lead-monolayer heterostructure stacked on a SiC substrate. Using synchrotron-based angle-resolved photoemission spectroscopy, we analyze the band structure of each layer, focusing on the charge transfer from K to the underlying 2D layers. Since K forms a $(2 \times 2)$ overlayer with respect to graphene, the amount of charge carriers donated by K can be determined. Our findings reveal that adsorption of K not only leads to a significant $n$-doping of the adjacent graphene layer but also to an electron transfer into the Pb monolayer. Remarkably, $\approx 44\%$ of the electrons donated by the K adlayer are transferred into its second nearest neighbouring layer, i.e. Pb, while $\approx 56\%$ remain in the graphene.