Tunnelling defect nanoclusters in hcp 4He crystals: alternative to   supersolidity
  A simple model based on the concept of resonant tunnelling clusters of lattice defects is used to explain the low temperature anomalies of hcp 4He crystals (mass decoupling from a torsional oscillator, shear modulus anomaly, dissipation peaks, heat capacity peak). Mass decoupling is a result of an internal Josephson effect: mass supercurrent inside phase coherent tunnelling clusters. Quantitative results are in reasonable agreement with experiments. 
A. F. Andreev
cond-mat.other