Condensation of helium in nanoscopic alkali wedges at zero temperature

TL;DR

This paper models the structure of liquid helium confined in nanoscopic alkali wedges at zero temperature, revealing how wedge angle influences wetting behavior and phase transitions, with implications for understanding helium adsorption on alkali surfaces.

Contribution

It provides a detailed density functional analysis of helium in nanoscopic wedges, identifying stable states and phase transitions, and proposes a new criterion for contact angle determination.

Findings

Wedge angle affects helium meniscus shape and wetting behavior.

Cesium wedges exhibit filling and emptying transitions at specific angles.

A new criterion for helium contact angle on cesium is introduced.

Abstract

We present a complete calculation of the structure of liquid $^4$He confined to a concave nanoscopic wedge, as a function of the opening angle of the walls. This is achieved within a finite-range density functional formalism. The results here presented, restricted to alkali metal substrates, illustrate the change in meniscus shape from rather broad to narrow wedges on weak and strong alkali adsorbers, and relate this change to the wetting behavior of helium on the corresponding planar substrate. As the wedge angle is varied, we find a sequence of stable states that, in the case of cesium, undergo one filling and one emptying transition at large and small openings, respectively. A computationally unambiguous criterion to determine the contact angle of $^4$He on cesium is also proposed.