Critical flow and dissipation in a quasi-one-dimensional superfluid

Area of Science:

• Condensed Matter Physics
• Quantum Fluids
• Critical Phenomena

Background:

• Superfluidity in Helium-4 (⁴He) exemplifies universal critical phenomena, sharing a universality class with XY ferromagnetism.
• Reduced dimensionality is expected to inhibit superfluidity due to enhanced fluctuations.

Purpose of the Study:

• Investigate the behavior of superfluid velocity in confined geometries approaching one-dimensional (1D) limits.
• Explore deviations from bulk superfluidity in nanoscale channels.

Main Methods:

• Measured liquid helium flow rate in single nanopores (3 nm to 20 nm radius).
• Deduced superfluid velocity (v s) from flow rate measurements.
• Analyzed pressure and temperature dependence of superfluid velocity.

Main Results:

• Observed suppression of pressure dependence of superfluid velocity as pore size decreased.
• Found temperature dependence of v s fits a single power-law exponent over a wide range.
• Noted decreasing critical velocities with decreasing radius below ~20 nm, contrasting with bulk behavior.

Conclusions:

• Deviations indicate a crossover to a quasi-1D state in nanopores.
• Channel radius acts as a cutoff for critical topological defect size.
• Confined geometries significantly alter superfluid critical phenomena.