A Gross-Pitaevskii Treatment for Supersolid He
  The observations of non-linear rotational susceptibility (NCRI) in samples of solid He below 1-200 mK temperatures are conjectured to be describable in terms of a rarified Gross-Pitaevskii superfluid of vacancies (or, more generally, incommensuracies) with a transition temperature of about 50 mK, whose density is locally enhanced by crystal imperfections. We argue that the observations can be much affected by this density enhancement. We argue also that it is likely that the ground state of every pure Bose solid is supersolid. 
Philip W Anderson