Critical dislocation speed in helium-4 crystals

Abstract

Our experiments show that in ${}^4$He crystals, the binding of ${}^3$He impurities to dislocations does not necessarily imply their pinning. Indeed, in these crystals, there are two different regimes of the motion of dislocations when impurities bind to them. At lowdriving strain $\epsilon$ and frequency $\omega$, where the dislocation speed is less than a critical value (45 $\mu$m/s), dislocations and impurities apparently move together. Impurities really pin the dislocations only at higher values of $\omega$. The critical speed separating the two regimes is two orders of magnitude smaller than the average speed of free ${}^3$He impurities in the bulk crystal lattice.We obtained this result by studying the dissipation of dislocation motion as a function of the frequency and amplitude of a driving strain applied to a crystal at low temperature. Our results solve an apparent contradiction between some experiments, which showed a frequency-dependent transition temperature from a soft to a stiff state, and other experiments or models where this temperature was assumed to be independent of frequency. The impurity pinning mechanism for dislocations appears to be more complicated than previously assumed.

References in corpus (5)

• Low Temperature Shear Modulus Changes in Solid 4-He and Connection to Supersolidity
• Absence of supersolidity in solid helium in porous Vycor glass
• The giant plasticity of a quantum crystal
• Non-linear Elastic Response in Solid Helium: critical velocity or strain
• Binding of a 3He impurity to a screw dislocation in solid 4He

Cited by in corpus (12)

• Simulation and understanding of quantum crystals
• Dislocation networks in helium-4 crystals
• Multiple Mode Torsional Oscillator Studies and Evidence for Supersolidity in Bulk 4He
• Frequency-dependent Study of Solid Helium-4 Contained in a Rigid Double-torus Torsional Oscillator
• No Effect of Steady Rotation on Solid ${}^4$He in a Torsional Oscillator
• Superfluid-like TO Responses in Rotating Solid Helium
• Characterization of the Surface of Moving solid 4He
• Simultaneous investigation of shear modulus and torsional resonance of solid 4He
• Transverse Quantum Superfluids
• Dislocation Mobility and Anomalous Shear Modulus Effect in ${}^4$He Crystals
• Superfluid Field response to Edge dislocation motion
• Low frequency elastic measurements on solid ${}^4$He in Vycor using a torsional oscillator