Phonon lineshapes in atom-surface scattering

TL;DR

This paper models phonon lineshapes in atom-surface scattering using a stochastic approach based on the Caldeira-Leggett Hamiltonian, incorporating effects of adsorbates through an extended two-bath model.

Contribution

It introduces a simple stochastic model for phonon lineshapes and extends it to include adsorbate effects with a two-bath framework.

Findings

Phonon frequencies are renormalized by damping coefficients.

The model captures lineshape modifications due to adsorbates.

Extension to two baths accounts for adsorbate-induced effects.

Abstract

Phonon lineshapes in atom-surface scattering are obtained from a simple stochastic model based on the so-called Caldeira-Leggett Hamiltonian. In this single-bath model, the excited phonon resulting from a creation or annihilation event is coupled to a thermal bath consisting of an infinite number of harmonic oscillators, namely the bath phonons. The diagonalization of the corresponding Hamiltonian leads to a renormalization of the phonon frequencies in terms of the phonon friction or damping coefficient. Moreover, when there are adsorbates on the surface, this single-bath model can be extended to a two-bath model accounting for the effect induced by the adsorbates on the phonon lineshapes as well as their corresponding lineshapes.