Surface Phase Transitions Induced by Electron Mediated Adatom-Adatom Interaction

TL;DR

This paper presents a theory explaining surface phase transitions in metallic adatom layers driven by electron-mediated interactions, accounting for observed structural changes in specific surface systems.

Contribution

It introduces a model linking electron-mediated adatom interactions to surface phase transitions, explaining experimental observations in Sn/Ge(111) and Pb/Ge(111).

Findings

The indirect adatom-adatom interaction causes structural phase transitions.

Phonon instability triggers the transition when interaction dominates.

Theory explains all salient features of observed surface transitions.

Abstract

We propose that the indirect adatom-adatom interaction mediated by the conduction electrons of a metallic surface is responsible for the $\sqrt{3}\times \sqrt{3}\Leftrightarrow 3\times 3$ structural phase transitions observed in Sn/Ge (111) and Pb/Ge (111). When the indirect interaction overwhelms the local stress field imposed by the substrate registry, the system suffers a phonon instability, resulting in a structural phase transition in the adlayer. Our theory is capable of explaining all the salient features of the $\sqrt{3}\times \sqrt{3}\Leftrightarrow 3\times 3$ transitions observed in Sn/Ge (111) and Pb/Ge (111), and is in principle applicable to a wide class of systems whose surfaces are metallic before the transition.