Low Temperature Shear Modulus Changes in Solid 4-He and Connection to Supersolidity

Abstract

Superfluidity, liquid flow without friction, is familiar in helium. The first evidence for "supersolidity", its analogue in quantum solids, came from recent torsional oscillator (TO) measurements involving 4-He. At temperatures below 200 mK, TO frequencies increased, suggesting that some of the solid decoupled from the oscillator. This behavior has been replicated by several groups but solid 4-He does not respond to pressure differences and persistent currents and other signatures of superflow have not been seen. Both experiments and theory indicate that defects are involved. These should also affect the solid's mechanical behavior and so we have measured the shear modulus of solid 4-He at low frequencies and strains. We observe large increases below 200 mK, with the same dependence on measurement amplitude, 3-He impurity concentration and annealing as the decoupling seen in TO experiments. This unusual elastic behavior is explained in terms of a dislocation network which is pinned by 3-He at the lowest temperatures but becomes mobile above 100 mK. The frequency changes in TO experiments appear to be related to the motion of these dislocations, perhaps by disrupting a possible supersolid state.

18 pages, 4 figues, Supplementary Information

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Cited by in corpus (13)

• Observation of Unusual Mass Transport in Solid hcp 4He
• Evidence for a Superglass State in Solid 4He
• The effect of 3He impurities on the nonclassical response to oscillation of solid 4He
• Probing the Upper Limit of Nonclassical Rotational Inertia
• Solid 4He and the Supersolid Phase: from Theoretical Speculation to the Discovery of a New State of Matter? A Review of the Past and Present Status of Research
• Thermal History of Solid 4He Under Oscillation
• Dynamical creation of a supersolid in asymmetric mixtures of bosons
• Binding of a 3He impurity to a screw dislocation in solid 4He
• Torsional oscillator and synchrotron x-ray experiments on solid 4He in aerogel
• New Dissipation Relaxation Phenomenon in Oscillating Solid He-4
• Finite size Berezinski-Kosterlitz-Thouless transition at grain boundaries in solid ${}^4$He and role of ${}^3$He impurities
• Ultrasound study of the solid-liquid transition and solid-liquid interface of ${}^4$He in aerogels
• Quantum plasticity and dislocation-induced supersolidity