The observation of reduced rotational inertia in a cell containing solid ${}^4\mathrm{He}$ has been interpreted as evidence for superfluidity of the solid. We propose an alternative explanation: slippage of the solid, due to grain boundary premelting between the solid and dense adsorbed layers at the container wall. We calculate the range of film thickness, and determine the viscosity that will account for the missing rotational inertia. Grain boundary premelting also explains inertial anomalies in an earlier study of solid helium in porous glass and indicates that the liquid is partially superfluid.

• Received 23 December 2004

DOI:https://doi.org/10.1103/PhysRevLett.94.235301