Superfluidity and quantum melting of p-H2 clusters.

Structural and superfluid properties of p-H2 clusters of size up to N=40 molecules, are studied at low temperature (0.5 K<or=T<or=4 K) by path integral Monte Carlo simulations. The superfluid fraction rhoS(T) displays an interesting, nonmonotonic behavior for 22<or=N<or=30. We interpret this dependence in terms of variations with N of the cluster structure. Superfluidity is observed at low T in clusters of as many as 27 molecules; in the temperature range considered here, quantum melting is observed in some clusters, which are seen to freeze at high temperature.