Low-temperature shear modulus changes in solid 4He and connection to supersolidity

@article{Day2007LowtemperatureSM,
  title={Low-temperature shear modulus changes in solid 4He and connection to supersolidity},
  author={James Day and John Beamish},
  journal={Nature},
  year={2007},
  volume={450},
  pages={853-856}
}
Superfluidity—liquid flow without friction—is familiar in helium. The first evidence for ‘supersolidity’, its analogue in quantum solids, came from torsional oscillator measurements involving 4He. At temperatures below 200 mK, the torsional oscillator frequencies increased, suggesting that some of the solid decoupled from the oscillator. This behaviour has been replicated by several groups, but solid 4He does not respond to pressure differences, and persistent currents and other signatures of… 

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