Van der Waals-Casimir-Polder interaction of an atom with a composite surface

TL;DR

This paper investigates how nonlocal electrodynamics, including bulk and surface diffusion models, affect the van der Waals and Casimir-Polder interactions between an atom and a metal surface, revealing potential for surface state probing.

Contribution

It introduces nonlocal models of electron diffusion into vdW-CP interaction calculations, showing continuous transition to semiconductors and sensitivity to surface states.

Findings

Transition to semiconductors is continuous with conductivity.

vdW-CP data can distinguish between bulk and surface diffusion.

Surface states can be probed via atom-surface dispersion interactions.

Abstract

We study the dispersion interaction of the van der Waals and Casimir-Polder (vdW-CP) type between a neutral atom and the surface of a metal by allowing for nonlocal electrodynamics, i.e. electron diffusion. We consider two models: (i) bulk diffusion, and (ii) diffusion in a surface charge layer. In both cases the transition to a semiconductor is continuous as a function of the conductivity, unlike the case of a local model. The relevant parameter is the electric screening length and depends on the carrier diffusion constant. We find that for distances comparable to the screening length, vdW-CP data can distinguish between bulk and surface diffusion, hence it can be a sensitive probe for surface states.