Giant plasticity of a quantum crystal

Area of Science:

• Condensed matter physics
• Materials science
• Quantum crystals

Background:

• Crystalline materials typically deform irreversibly under stress at high temperatures due to dislocation motion.
• Plasticity in conventional crystals is a well-studied phenomenon linked to defect movement.
• Understanding deformation mechanisms in exotic materials is crucial for materials science.

Purpose of the Study:

• To investigate the mechanical properties of pure helium 4 crystals at low temperatures.
• To characterize the phenomenon of giant plasticity observed in helium 4.
• To determine the factors influencing the reversibility and anisotropy of this plasticity.

Main Methods:

• Experiments were conducted on oriented single crystals of helium 4.
• Measurements focused on the crystal's resistance to shear under stress.
• The study examined the effects of impurities (helium 3) and temperature (thermal phonons) on plasticity.

Main Results:

• Helium 4 crystals display significant, anisotropic, and reversible plasticity at zero temperature.
• A near-complete loss of shear resistance was observed in a specific crystallographic direction.
• Dislocations were found to glide unimpeded along basal planes in the hexagonal structure.
• The observed plasticity vanished with the introduction of helium 3 impurities or thermal phonons.

Conclusions:

• Pure helium 4 exhibits unique quantum plasticity driven by dislocation glide.
• This plasticity is highly sensitive to impurities and thermal effects, highlighting quantum phenomena.
• The findings offer insights into the behavior of quantum solids under stress.