Quantum threshold reflection of He atom beams from rough surfaces

TL;DR

This study models quantum reflection of helium atom beams from various surfaces, revealing deviations from linear behavior at higher incident angles and suggesting surface roughness has minimal impact, challenging previous experimental claims.

Contribution

It provides a theoretical analysis of quantum reflection that differs from prior experimental interpretations, especially regarding the role of surface roughness and the quantum-classical transition.

Findings

Reflection probability depends linearly on incident wave vector at small values.

Deviations from linearity occur at larger incident wave vectors, approaching quadratic dependence.

Surface roughness has negligible effect on quantum reflection in the studied conditions.

Abstract

Quantum reflection of thermal He atoms from various surfaces (glass slide, GaAs wafer, flat and structured Cr) at grazing conditions is studied within the elastic close-coupling formalism. Comparison with the experimental results of B.S. Zhao et al, Phys. Rev. Lett. {\bf 105}, 133203 (2010) is quite reasonable but the conclusions of the present theoretical analysis are different from those discussed in the experimental work. The universal linear behavior observed in the dependence of the reflection probability on the incident wave vector component perpendicular to the surface is only valid at small values of the component whereas, at larger values, deviation from the linearity is evident, approaching a quadratic dependence at higher values. The surface roughness seems to play no important role in this scattering. Moreover, the claim that one observes a transition from quantum to classical reflection seems to be imprecise.