Pb-intercalated epitaxial graphene on SiC: Full insight into band structure and orbital character of interlayer Pb, and charge transfer into graphene

TL;DR

This study uses ARPES and DFT to analyze the band structure and orbital character of Pb intercalated between epitaxial graphene and SiC, revealing charge transfer and potential proximity effects.

Contribution

It provides a comprehensive experimental and theoretical analysis of interlayer Pb in epitaxial graphene on SiC, highlighting orbital interactions and charge transfer mechanisms.

Findings

Pb exhibits metallic character with free electron-like bands.

Pb bands have a predominant out-of-plane orbital character.

Charge transfer occurs from Pb and SiC to graphene.

Abstract

Intercalation is a robust approach for modulating the properties of epitaxial graphene on SiC and stabilizing two-dimensional (2D) intercalant layers at the graphene/SiC interface. In this work, we present synchrotron-based angle resolved photoelectron spectroscopy (ARPES) measurements focussing on the band structure of intercalated Pb under a single layer of epitaxial graphene. The interlayer Pb exhibits a metallic character, a $(1 \times 1)$ registry with respect to SiC, and free electron-like bands to a first order. Divergences from the free electron approximation include various band splittings and gaps throughout the Pb Brillouin zone. Light polarization dependent ARPES measurements indicate a predominant out-of-plane orbital character for the Pb bands, suggesting potential interactions between the interlayer Pb and graphene's $\pi$ orbitals that may induce proximity effects in graphene. Density functional theory (DFT) calculations for a $(1 \times 1)$ Pb monolayer on SiC show a reasonable qualitative agreement with the experimentally observed interlayer bands as well as the polarization dependent measurements. Finally, temperature dependent ARPES measurements reveal that the nearly charge-neutral graphene layer involves charge transfer from both the interlayer Pb and the substrate SiC.