  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.
