Superfluid response of two-dimensional parahydrogen clusters in confinement

TL;DR

This study uses computer simulations to explore how confinement affects superfluidity in small 2D parahydrogen clusters, revealing their resilience and potential for a superfluid cluster crystal phase.

Contribution

It demonstrates that small 2D parahydrogen clusters maintain superfluidity under confinement and suggests the possibility of a stable superfluid cluster crystal phase.

Findings

Superfluid response remains strong in small clusters under various confinement conditions.

Clusters of about ten molecules may form a thermodynamically stable superfluid phase.

Potential for tunnelling across unit cells indicates a superfluid cluster crystal phase.

Abstract

We study by computer simulations the effect of confinement on the superfluid properties of small two-dimensional (2D) parahydrogen clusters. For clusters of fewer than twenty molecules, the superfluid response in the low temperature limit is found to remain comparable in magnitude to that of free clusters, within a rather wide range of depth and size of the confining well. The resilience of the superfluid response is attributable to the "supersolid" character of these clusters. We investigate the possibility of establishing a bulk 2D superfluid "cluster crystal" phase of \paraH2, in which a global superfluid response would arise from tunnelling of molecules across adjacent unit cells. The computed energetics suggests that for clusters of about ten molecules, such a phase may be thermodynamically stable against the formation of the equilibrium insulating crystal, for values of the cluster crystal lattice constant possibly allowing tunnelling across adjacent unit cells