Third sound and stability of 3 He-4 He mixture films
Eckhard Krotschecka , Roger Andersonb , and Michael Millerb
a
b
Institut für Theoretische Physik, Johannes Kepler Universität, A 4040 Linz, Austria
Department of Physics, Washington State University, Pullman, WA 99164-2814, USA
We study third sound and the interaction between 3 He adatoms in thin 3 He-4 He mixture films from both a
first-principles, microscopic theory. Utilizing the variational, hypernetted chain/Euler-Lagarange (HNC–
EL) theory as applied to inhomogeneous boson systems, we calculate chemical potentials for both the 4 He
superfluid film and the physisorbed 3 He. Numerical density derivatives of the chemical potentials lead to
the sought-after third sound speeds that clearly reflect a layered structure of at least seven oscillations.
In this paper, we report third sound on four model substrates: Nuclepore, glass, lithium, and sodium.
We find, that the effect of the 3 He depends sensitively on the particular 4 He film coverage. The third
sound speed can either increase or decrease. In fact, in some regimes, the added 3 He destabilizes the
film and can drive “layering transitions” leading to fairly complicated geometric structures of the film in
which the outermost layer actually consists of phase–separated regimes of 3 He and 4 He. We also study
the dimerization of 3 He in Andreev states due to ripplon exchange.
Sorting category: Ac Quantum gases, fluids and solids
Keywords: Helium films, third sound, correlated basis functions
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