Local Superfluidity of Parahydrogen Clusters

We study by Quantum Monte Carlo simulations the local superfluid response of small (up to 27 molecules) parahydrogen clusters, down to temperatures as low as 0.05 K. We show that at low temperature superfluidity is not confined at the surface of the clusters, as recently claimed by Khairallah et al. [Phys. Rev. Lett. 98, 183401 (2007)]. Rather, even clusters with a pronounced shell structure are essentially uniformly superfluid. Superfluidity occurs as a result of long exchange cycles involving all molecules.