Mass flux and solid growth in solid ⁴He for 60-700 mK

Area of Science:

• Condensed Matter Physics
• Low-Temperature Physics
• Quantum Materials

Background:

• Understanding atomic transport phenomena in solid helium is crucial for quantum fluid dynamics.
• The behavior of hexagonal close-packed (hcp) solid ⁴He at millikelvin temperatures presents unique challenges.
• Previous studies have explored various properties, but the precise conditions for mass flux remain under investigation.

Purpose of the Study:

• To confirm and characterize atomic flux in hcp solid ⁴He using the thermomechanical effect.
• To investigate the temperature dependence of this mass flux, particularly near 80 mK.
• To determine the influence of sample preparation temperature on subsequent mass transport properties.

Main Methods:

• Utilized the thermomechanical effect as a probe for atomic flux.
• Experimentally controlled and measured temperature ranges down to 60 mK.
• Prepared solid ⁴He samples at different initial temperatures (60 mK, >300 mK) for comparative analysis.

Main Results:

• Confirmed the existence of atomic flux in hcp solid ⁴He below approximately 600 mK.
• Observed an abrupt decrease in flux near 80 mK, followed by an increase upon further cooling.
• Found that samples freshly prepared at 60 mK exhibited no mass flux and could not be grown, unlike those prepared at higher temperatures.

Conclusions:

• The thermomechanical effect provides definitive evidence of atomic flux in hcp solid ⁴He.
• Sample preparation temperature significantly impacts the ability of solid ⁴He to sustain mass flux at low temperatures.
• The observed flux behavior suggests complex underlying mechanisms related to crystal growth and defects in solid helium.