Observation of Classical Rotational Inertia and Nonclassical Supersolid   Signals in Solid 4He below 250 mK
  We have confirmed the existence, as first reported by Kim and Chan, of a supersolid state in solid 4He at temperatures below 250 mK. We have employed a torsional oscillator cell with a square cross section to insure a locking of the solid to the oscillating cell. We find that NCRI signal is not a universal property of solid 4He, but can be eliminated through an annealing of the solid helium sample. This result has important implications for the nature of the supersolid state. 
Ann Sophie C. Rittner and John D. Reppy