UNIVERSITY OF CALIFORNIA AT BERKELEY

PACKARD GROUP

Third Sound in Superfluid 3He  

RESEARCH TEAM

   GRADUATE STUDENTS:

  • Joan A. Hoffman
  • Ray W. Simmonds

   POST-DOC RESEARCHERS:

   PRINCIPAL  INVESTIGATORS:

   PAST RESEARCHERS:

RESEARCH SUMMARY

   What is Third Sound?
   Unconventional Superfluidity in 3He
   Experimental Design
   Results: Third Sound Spectra
   Results: New Information - c3 & rs
   Future Experiments

RELEVANT PUBLICATIONS

QUICK OVERVIEW

Third sound is a surface wave on a superfluid film, which occurs despite the fact that the film is so thin that viscosity prevents all normal motion. It has been known and used for decades as a tool for studying superfluid 4He, and it has just recently been observed for the first time in superfluid 3He films by this research group.

3He  is a remarkable material, a neutral, Fermi liquid which becomes superfluid at low temperatures by a BCS pairing mechanism. The details of this transition, and the behavior of the superfluid state, are related to the superconductivity now being studied in unconventional, high-temperature superconductors. Studies of 3He  promise to shed light on this important topic.

We designed an experimental cell to generate and detect third sound waves in 3He films at temperatures near 300 mK.

We obtained spectra showing resonances in the surface motion of the film, as a function of frequency, which behave as expected for third sound waves. This is the first evidence for the existence of third sound waves in superfluid 3He films.  From these spectra, we were able to obtain new physical information; in particular the speed of third sound and the average superfluid density of the films, for a range of temperatures and film thicknesses.

Finally, there are a variety of experiments which we are planning to carry out in the near future, which the existence of third sound as a probe should make possible for the first time.
    

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