Metastable solid⁴He and the possible role of point defects

Area of Science:

• Condensed Matter Physics
• Quantum Materials Science

Background:

• Solid helium-4 exhibits a metastable phase, crucial for understanding quantum fluid behavior.
• Point defects are hypothesized to play a role in the destabilization of this phase.

Purpose of the Study:

• Investigate the role of point defects in destabilizing the metastable phase of solid helium-4.
• Determine the pressure at which vacancy and self-interstitial formation energies become zero.

Main Methods:

• Employed a trial function of the shadow class with an explicit symmetrical kernel.
• This function effectively handles atomic exchange and defect delocalization.
• Calculated formation energies for vacancies, self-interstitials, and impurities.

Main Results:

• Identified a critical pressure (Pc = 20±2 atm) where vacancy formation energy is zero, aligning with experimental observations.
• Found that self-interstitial formation energy becomes zero at densities where vacancies also exhibit zero formation energy.
• Estimated formation energies for helium-3 (³He) interstitials and substitutional impurities.

Conclusions:

• The study confirms the significant role of point defects in the destabilization of solid helium-4's metastable phase.
• The calculated critical pressures provide valuable benchmarks for experimental verification.
• The theoretical framework offers insights into the behavior of impurities and defects in quantum solids.