Plastic Deformation in a Quantum Solid: Dislocation Avalanches and Creep in Helium

Area of Science:

• Solid-state physics
• Quantum materials science
• Low-temperature physics

Background:

• Conventional solids exhibit elastic and plastic deformation governed by dislocation motion.
• Understanding plasticity in quantum solids is crucial for exploring unique defect behaviors.
• Helium-4 (He) offers a unique system dominated by quantum effects at low temperatures.

Purpose of the Study:

• To investigate plastic deformation and dislocation dynamics in hexagonal close-packed (hcp) solid He.
• To identify and characterize "metallurgical" phenomena, such as dislocation avalanches, in a quantum solid.
• To explore the transition from avalanche behavior to continuous creep in hcp He.

Main Methods:

• Experiments conducted on hcp He below 0.4 K.
• Measurement of stress-strain relationships and acoustic emissions.
• Observation of slip event dimensions and creep behavior at various temperatures.

Main Results:

• A strain threshold for elastic deformation was identified, leading to sudden stress drops and acoustic emissions.
• Dislocation avalanches with dimensions ranging from millimeters to microns were observed.
• At higher temperatures, avalanches transitioned to continuous creep, with steady flow observed at stresses as low as 400 Pa.

Conclusions:

• Quantum effects significantly influence defect behavior in hcp He, leading to plasticity analogous to conventional metals.
• Dislocation avalanches represent a key mechanism of plastic deformation in this quantum solid.
• The observed transition to continuous creep highlights the temperature-dependent nature of dislocation dynamics in quantum solids.