Low Temperature Physics: 34, 340 (2008); https://doi.org/10.1063/1.2911652 (4 pages)
Физика Низких Температур: Том 34, Выпуск 4-5 (Апрель 2008), c. 427-430    ( к оглавлению , назад )

Defects and supersolidity: effects of annealing and stress on elastic behavior of solid 4He

A. Syshchenko, J. Day, and J. Beamish

Department of Physics, University of Alberta, Edmonton, Alberta T6G 2G7, Canada
E-mail: beamish@phys.ualberta.ca

Received December 3, 2007


Recent measurements showed that solid 4He can decouple from a torsional oscillator below 200 mK and defects appear to be crucial to this behavior. Helium’s shear modulus increases in the same range, which can be understood in terms of dislocations pinned by 3He impurities at the lowest temperatures, but mobile above 100 mK. We have measured helium’s pressure and shear modulus to study the effects of annealing and stresses applied at low temperatures. Pressure gradients produced during crystal growth or plastic deformation are greatly reduced by annealing, but only at temperatures close to melting. Annealing does not change the low-temperature modulus but usually raises it at high temperature, as expected if annealing eliminates some dislocations. Large stresses also affect the modulus, but these changes are reversed by heating above 0.5 K, suggesting that defects introduced by stress are easier to anneal than those produced during growth.

PACS: 67.80.bd Superfluidity in solid 4He, supersolid 4He;
PACS: 67.80.dj Defects, impurities, and diffusion;
PACS: 67.80.de Structure, lattice dynamics and sound.

Key words: solid helium, supersolid, quantum solid, dislocations, shear modulus, annealing, plastic deformation.