Non-classical rotational inertia in the supersolid state
  An abrupt drop in the moment of inertia recently found in solid helium 4 is explained in terms of dynamics of zero-point vacancies (ZPV). Mechanical decoupling of ZPV from the motion of the container due to Bose statistics is developed to a macroscopic phenomenon by repulsive interaction. It gives a negative answer to the question whether BEC is a necessary condition for non-classical rotational inertia in a bulk three-dimensional system. 
Shun-ichiro Koh