Surface-Dominated Finite-Size Effects in Nanoconfined Superfluid Helium

Area of Science:

• Condensed Matter Physics
• Quantum Fluids
• Nanoscale Science

Background:

• Superfluid helium-4 (He II) is a key system for studying quantum phenomena in confined spaces.
• Finite-size effects in strongly confined geometries remain an active area of research.
• Understanding superfluid behavior in nanoconfinement is crucial for developing new quantum technologies.

Purpose of the Study:

• To investigate the superfluid density of He II in millimeter-scale channels with heights of 25 and 50 nm.
• To explore the impact of high pressures on confined superfluid helium.
• To elucidate the mechanisms behind the suppression of superfluid density in nanoconfined geometries.

Main Methods:

• Utilized a nanofluidic Helmholtz resonator to study He II.
• Experimentally measured superfluid density in precisely controlled nanoscale channels.
• Analyzed data from the transition temperature down to 0.6 K at high pressures.

Main Results:

• Observed a measurable suppression of superfluid density in confined He II.
• Quantified the suppression from the superfluid transition temperature down to 0.6 K.
• Attributed the suppression to rotonlike thermal excitations with a 5 K energy gap.

Conclusions:

• Surface-bound excitations are responsible for the observed suppression of superfluid density.
• These excitations explain the previously unexplained lack of finite-size scaling.
• The findings provide critical insights into quantum fluid behavior at the nanoscale.