Unveiling the origin of the linear dispersion in silicene/Ag(111)

The band structure of the recently synthesized (3$\times$3) silicene monolayer on (4$\times$4) Ag(111) is investigated using density functional theory. To compare to recent angle-resolved photoemission spectroscopy (ARPES) experiments [Phys.\ Rev.\ Lett.\ {\bf 108}, 155501 (2012)], including the photon energy ($k_\perp$) dependence of the spectra, we use a $k$-projection technique to unfold the supercell bands of both silicene and the substrate onto the corresponding primitive cells. Our calculations reproduce the observed linear dispersion across the K point of (1$\times$1) silicene observed, but demonstrate that this is not a Dirac state, but rather originates from the Ag(111) substrate, thus resolving the controversy concerning the origin of the linear dispersion in silicene/Ag(111).