Quantum sticking, scattering and transmission of 4He atoms from superfluid 4He surfaces

TL;DR

This paper presents a microscopic theory for the scattering, transmission, and sticking of helium-4 atoms on superfluid helium surfaces, emphasizing multiparticle interactions and inelastic processes.

Contribution

It introduces a comprehensive microscopic model that incorporates mode coupling and inelastic effects, advancing understanding of atom-surface interactions in superfluid helium.

Findings

Coupling to surface excitations affects atom transmission.

Energy loss mechanisms are significant in scattering processes.

Inelastic effects modify the excitation spectrum near the surface.

Abstract

We develop a microscopic theory of the scattering, transmission, and sticking of 4He atoms impinging on a superfluid 4He slab at near normal incidence, and inelastic neutron scattering from the slab. The theory includes coupling between different modes and allows for inelastic processes. We find a number of essential aspects that must be observed in a physically meaningful and reliable theory of atom transmission and scattering; all are connected with multiparticle scattering, particularly the possibility of energy loss. These processes are (a) the coupling to low-lying (surface) excitations (ripplons/third sound) which is manifested in a finite imaginary part of the self energy, and (b) the reduction of the strength of the excitation in the maxon/roton region.