Metastable impurity-helium solid phase. Experimental and theoretical evidence

A novel solid metastable phase of “sticking-together” helium van der Waals coats surrounding polarizable heavy impurities - Ne, Ar, Kr, Xe, N and N₂ - has been obtained and investigated using the experimental technique based on gas beam injection into superfluid helium. The element composition for this phase was measured and for all inert gases the solid samples were found to consist of more than 90% helium atoms and to keep stability up to T ≈ 8 K. The cluster approach to the theoretical analysis of the model NeHe₁₂ structures developed makes it possible to suggest the main physical reason for its formation to be the breakdown of quantum-mechanical helium atoms behavior, namely, strong suppression of amplitudes of radial zeroth vibrations for helium atoms belonging to the van der Waals shell in the field of dispersion forces of the central impurity particle. The phase diagram for the impurity-helium substance has been simulated and the direction of future investigations have also been outlined.