Helium mass flow through a solid-superfluid-solid junction.

Area of Science:

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

Background:

• Superfluidity in helium-4 (⁴He) is a quantum mechanical phenomenon observed at very low temperatures.
• Understanding mass transport in solid helium, especially with impurities like helium-3 (³He), is crucial for fundamental physics.
• Previous experiments have explored flow through solid helium, but the precise limiting mechanisms remain debated.

Purpose of the Study:

• To investigate mass transport through a solid-superfluid-solid junction connecting two chambers of solid ⁴He via a Vycor channel.
• To determine the factors limiting the observed mass flow under varying temperature and ³He concentration conditions.

Main Methods:

• Experimental setup involved two chambers containing solid ⁴He connected by a Vycor channel.
• Mechanical squeezing of solid ⁴He in one chamber induced pressure changes in the second chamber, indicating mass transport.
• Experiments were conducted at low temperatures (starting around 600 mK) with controlled ³He impurity concentrations.

Main Results:

• Mass transport was observed, with pressure responses similar to previous studies.
• Flow initiated around 600 mK and increased with decreasing temperature.
• A dramatic decrease in flow occurred at a temperature T_d, which was dependent on the ³He concentration.

Conclusions:

• The experimental results suggest that mass transfer across the solid-liquid interface at the Vycor ends is the primary limitation.
• Helium-3 impurities accumulating at these interfaces at low temperatures significantly impact the flow dynamics.
• The flow is not limited by transport pathways within the bulk solid ⁴He.