Surface state scattering by adatoms on noble metals

TL;DR

This paper investigates how magnetic and non-magnetic adatoms on noble metal surfaces influence surface state electrons, revealing conditions under which localized resonances form below the surface band edge, supported by systematic theoretical analysis.

Contribution

It provides a detailed theoretical study of surface state scattering by adatoms on Cu(111), identifying specific adatoms that induce localized resonances and explaining their origin.

Findings

Ca and 3d adatoms create split-off states at the surface band bottom.

Ga and Ge do not produce split-off states when adsorbed on the surface.

Embedded Ga and Ge impurities induce split-off states, unlike 3d impurities.

Abstract

When surface state electrons scatter at perturbations, such as magnetic or nonmagnetic adatoms or clusters on surfaces, an electronic resonance, localized at the adatom site, can develop below the bottom of the surface state band for both spin channels. In the case of adatoms, these states have been found very recently in scanning tunneling spectroscopy experiments\cite{limot,olsson} for the Cu(111) and Ag(111) surfaces. Motivated by these experiments, we carried out a systematic theoretical investigation of the electronic structure of these surface states in the presence of magnetic and non-magnetic atoms on Cu(111). We found that Ca and all 3$d$ adatoms lead to a split-off state at the bottom of the surface band which is, however, not seen for the $sp$ elements Ga and Ge. The situation is completely reversed if the impurities are embedded in the surface: Ga and Ge are able to produce a split-off state whereas the 3$d$ impurities do not. The resonance arises from the s-state of the impurities and is explained in terms of strength and interaction nature (attraction or repulsion) of the perturbing potential.