Dislocation Structure and Mobility in hcp ^{4}He

Area of Science:

• Condensed Matter Physics
• Quantum Crystals
• Materials Science

Background:

• Dislocations in hexagonal close-packed (hcp) helium-4 (4He) are crucial for understanding its unique quantum properties.
• Recent experiments have observed giant plasticity and mass flow phenomena in hcp 4He, prompting further theoretical investigation.
• The precise core structure and mobility mechanisms of dislocations in hcp 4He remain areas of active research.

Purpose of the Study:

• To investigate the core structure and mobility of screw and edge basal-plane dislocations in hcp 4He.
• To provide theoretical insights into recent experimental findings on giant plasticity and mass flow in hcp 4He.
• To elucidate the role of dislocation core structure and quantum fluctuations in the extreme mobility observed.

Main Methods:

• Utilizing path-integral Monte Carlo (PIMC) simulations.
• Analyzing the dissociation of dislocations into partial dislocations and stacking faults.
• Quantifying the fluctuations of partial dislocation core positions.

Main Results:

• Both screw and edge basal-plane dislocations in hcp 4He are found to dissociate into nonsuperfluid Shockley partial dislocations.
• These partial dislocations are separated by stacking fault ribbons, indicating they are unlikely to form 1D channels with Lüttinger-liquid-like behavior.
• Substantial fluctuations in partial core positions were observed even without applied stress, suggesting negligible lattice resistance to their motion.
• The study highlights the combined influence of partial core structure and zero-point fluctuations on extreme dislocation mobility.

Conclusions:

• The dissociation of dislocations and significant core fluctuations are key to understanding the giant plasticity in hcp 4He.
• The findings support experimental observations of negligible lattice resistance to partial dislocation motion.
• Quantum effects, specifically zero-point fluctuations, play a critical role in the observed extreme mobility of dislocations in hcp 4He.