On the possible "supersolid" character of parahydrogen clusters

TL;DR

This study uses Quantum Monte Carlo simulations to explore the structural and superfluid properties of small parahydrogen clusters, revealing a potential supersolid state in a specific cluster size due to quantum effects.

Contribution

First detailed theoretical investigation of parahydrogen clusters' superfluid and solid-like behaviors, proposing a mesoscopic supersolid state at N=26.

Findings

N=25 and 27 clusters become liquid-like and superfluid at low temperature.

N=26 cluster remains rigid and solid-like, indicating a supersolid state.

Isotopic substitution supports the supersolid interpretation.

Abstract

We present results of a theoretical study of structural and superfluid properties of parahydrogen clusters comprising 25, 26 and 27 molecules at low temperature. The microscopic model utilized here is based on the Silvera-Goldman pair potential. Numerical results are obtained by means of Quantum Monte Carlo simulations, making use of the continuous-space Worm Algorithm. The clusters are superfluid in the low temperature limit, but display markedly different physical behaviours. For N=25 and 27, superfluidity at low temperature arises as clusters melt, i.e., become progressively liquid-like as a result of quantum effects. On the other hand, for N = 26 the cluster remains rigid and solid-like. We argue that this cluster can be regarded as a mesoscopic "supersolid". This physical picture is supported by results of simulations in which a single parahydrogen molecule in the cluster is isotopically substituted.