Heavy isotope6He:Properties of bulk system and of clusters

Abstract

We have theoretically revisited the heavy isotope of He, ${}^{6}\mathrm{He}.$ It was considered many years ago as a possible superfluid system, but its short lifetime makes any experiment rather difficult and theoretical predictions are not very favorable. We have applied the shadow wave-function technique to the study of bulk ${}^{6}\mathrm{He}$ and we have also studied clusters of ${}^{6}\mathrm{He}.$ We confirm that the ground state is solid but the energy difference between the two phases is rather small and the solid order is also inhibited in clusters of many hundreds of particles. From a study of the off-diagonal one-body density matrix we find that Bose-Einstein condensation is present in these clusters. Thus clusters of ${}^{6}\mathrm{He}$ offer the unique opportunity to study the evolution from a superfluid to a solid driven by size effect and the properties of a highly defected quantum solid.