Does Silicene on Ag(111) Have a Dirac Cone?

TL;DR

This study uses first-principles calculations to show that silicene on Ag(111) does not have a Dirac cone, and the observed linear dispersions are due to the substrate, clarifying a debated issue.

Contribution

It provides the first detailed theoretical analysis demonstrating the absence of a Dirac cone in silicene on Ag(111) using band structure unfolding and projection techniques.

Findings

Dirac cone in silicene on Ag(111) is destroyed

Linear dispersions originate from the Ag substrate

Clarifies the source of observed electronic features

Abstract

We investigate the currently debated issue of the existence of the Dirac cone in silicene on an Ag(111) surface, using first-principles calculations based on density functional theory to obtain the band structure. By unfolding the band structure in the Brillouin zone of a supercell to that of a primitive cell, followed by projecting onto Ag and silicene subsystems, we demonstrate that the Dirac cone in silicene on Ag(111) is destroyed. Our results clearly indicate that the linear dispersions observed in both angular-resolved photoemission spectroscopy (ARPES) [P. Vogt et al, Phys. Rev. Lett. 108, 155501 (2012)] and scanning tunneling spectroscopy (STS) [L. Chen et al, Phys. Rev. Lett. 109, 056804 (2012)] come from the Ag substrate and not from silicene.