Poster

Surface lattice dynamics of Cs

D. Campi¹, M. Bernasconi¹, G. Benedek^1,2, A. P. Graham³, and J. P. Toennies³

¹Dipartimento di Scienza dei Materiali, Universita di Milano-Bicocca, Via Cozzi 53, 20125 Milano, Italy

²Donostia International Physics Center (DIPC), University of the Basque Country (UPV-EHU), Paseo M. de Lardizabal 4, 20018 San Sebastián/Donostia, Spain

³Max Planck Institut fur Dynamik und Selbstorganisation, Bunsenstrasse 10, 37073 Gottingen, Germany

Recent studies of inelastic Helium atom scattering (HAS) from metal surfaces have shown that HAS intensities are determined by electron-phonon (e-p) interaction, i.e., by the surface charge oscillations produced by atomic vibrations. As a consequence HAS has the ability to reveal sub-surface vibrational modes, as deep as the e-p interaction range (quantum-sonar effect) [1]. In this respect it is natural to investigate the case of simple metal (alkali) surfaces, where the surface electron density appears perfectly flat to thermal He atom scattering as expected for highly delocalized electronis states, but electron-phonon interaction is not particularly strong. HAS experiments from 20 ML Cs / Pt(111) show the expected Rayleigh wave (RW) dispersion curve for Cs and the anomalous surface longitudinal resonance, which is normally localized, towards the zone boundary, on subsurface layers and is therefore excited via surface e-p interaction, An theoretical analysis based on density functional perturbation theory (DFPT) calculations is presented.

[1] G. Benedek, M. Bernasconi, K.-P. Bohnen, D. Campi, E. V. Chulkov, P. M. Echenique, R. Heid, I. Yu. Sklyadneva, and J. P. Toennies, Phys. Chem. Chem. Phys. 16, 7159-7172 (2014)