Realistic large-scale modeling of Rashba and induced spin-orbit effects in graphene/high-Z-metal systems

TL;DR

This study uses advanced density-functional theory calculations to model graphene on heavy metal surfaces, revealing that giant Rashba and spin-orbit effects observed experimentally are not present in realistic models.

Contribution

The paper provides a detailed, realistic modeling approach showing the absence of giant Rashba and spin-orbit effects in graphene/high-Z-metal systems, challenging previous experimental claims.

Findings

No giant Rashba splitting observed in models

Spin-orbit induced splitting is not present

Realistic models match experimental surface properties

Abstract

Graphene, as a material with a small intrinsic spin-orbit interaction of approximately 1 $\mu$eV, has a limited application in spintronics. Adsorption of graphene on the surfaces of heavy-metals was proposed to induce the strong spin-splitting of the graphene $\pi$-bands either via Rashba effect or due to the induced spin-orbit effects via hybridization of the valence band states of graphene and metal. The spin-resolved photoelectron spectroscopy experiments performed on graphene adsorbed on the substrates containing heavy elements demonstrate the "giant" spin-splitting of the $\pi$ states of the order of 100 meV in the vicinity of the Fermi level ($E_F$) and the K point. However, the recent scanning tunneling spectroscopy experiments did not confirm these findings, leaving the fact of the observation of the "giant" Rashba effect or induced spin-orbit interaction in graphene still open. Thus, a detailed understanding of the physics in such systems is indispensable. From a theory side this requires, first of all, correct modeling of the graphene/metal interfaces under study. Here we present realistic super-cell density-functional theory calculations, including dispersion interaction and spin-orbit interaction, for several graphene/high-Z-metal interfaces. While correctly reproduce the spin-splitting features of the metallic surfaces, their modifications under graphene adsorption and doping level of graphene, our studies reveal that neither "giant" Rashba- nor spin-orbit induced splitting of the graphene pi states around $E_F$ take place.