On the Possible Supersolid Character of Parahydrogen Clusters

We present results of a theoretical study of structural and superfluid properties of parahydrogen (p-H-2) 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 behaviors. For N = 25 and 27, superfluidity at low temperature arises as clusters melt, that is, 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 the cluster (p-H-2)(26) can be regarded as a mesoscopic supersolid. This physical picture is supported by results of simulations in which a single p-H-2 molecule in the cluster is isotopically substituted.