Superfluidity in Hydrogen-Deuterium Mixed Clusters

Abstract

Path-integral Monte Carlo calculations have been performed on para-H₂ clusters mixed with several ortho-D₂ molecules, (D₂)$_{N_{D}}$(H₂)$_{N_{H}}$ with 1≤N _D ≤5 and 10≤N _H ≤20, to study their superfluid behavior at low temperatures. It is found that heavier D₂ molecules are located near the center of the mixed cluster, and radial density distributions of D₂ and H₂ tend to separate from each other as the number of D₂ molecules increases. We have also found significant suppression of superfluidity at specific cluster sizes when compared to those of the neighboring sizes. This can be understood in terms of the magic number stability previously reported in hydrogen clusters. Finally we present the local superfluid density distributions in the mixed clusters, which shows uniform local superfluidity of H₂ except near D₂ molecules.