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Superfluidity in the Second Layer of ^{4}He on Graphite
Jun Usami1,2,3, Hiroshi Fukuyama1,2
1The University of Tokyo, Cryogenic Research Center, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
Physical Review Letters
|August 10, 2026
Summary
Researchers discovered a new superfluid phase in helium-4 on graphite, exhibiting superfluidity and viscoelasticity. This finding supports the "superfluid liquid-crystal" hypothesis and clarifies previous observations of helium superfluid density.
Area of Science:
- Condensed Matter Physics
- Quantum Fluids
- Materials Science
Background:
- Previous studies on second-layer 4He on graphite suggested a superfluid phase but were limited by substrate uncertainties.
- The behavior of quantum fluids at low temperatures is crucial for understanding fundamental physics.
Purpose of the Study:
- To investigate the nature of the superfluid phase in second-layer 4He on graphite.
- To resolve substrate-related uncertainties in previous studies.
- To test the
- superfluid liquid-crystal
- hypothesis.
Main Methods:
- Simultaneous measurements of torsional-oscillator response and heat capacity.
- Experiments conducted on the same sample down to 30 mK.
- Random-Josephson-network analysis.
Main Results:
- Evidence for a new superfluid phase in second-layer 4He on graphite.
- This phase exhibits both superfluidity and enhanced viscoelasticity.
- The new phase is stable over a finite interval of 4He areal density.
- Substrate imperfections likely cause the previously reported log-T dependence of superfluid density.
Conclusions:
- The findings strongly support the
- superfluid liquid-crystal
- hypothesis.
- The study clarifies the behavior of quantum fluids on substrates.
- Identified a new superfluid phase with unique properties.
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