Local solid order around impurities: doped clusters and ions in He-4

We have studied the local solid order which is present around an alkaline ion in liquid He-4 and around a strong binding impurity like SF6, in an He-4 cluster at T = 0 K. We have treated on the same footing the solid order as well as the liquid one. This is achieved with the variational shadow wave function technique in which localization of particles arises from correlations. We determine the local order by studying the angular correlations among three atoms around the impurity. In the case of SF6 in an He-4 cluster we find a solid shell of 20 atoms. In the case of K+ in liquid He-4 we find two solid shells, the first with 12 atoms and the second with about 31. This snowball has a radius of about 7 Angstrom as suggested by experiment. We have computed also the excitation spectrum of the K+ impurity and we find an effective mass of 55 He-4 masses. (C) 2000 Published by Elsevier Science B.V. All rights reserved.