- Conference date: 10-17 August 2005
- Location: Orlando, Florida (USA)
We study third sound and the interaction between 3He adatoms in two thin 3He‐4He mixture films from a first‐principles, microscopic theory. Utilizing the variational, hypernetted‐chain Euler‐Lagrange (HNC‐EL) theory as applied to inhomogeneous boson systems, we calculate chemical potentials for both the 4He superfluid film and the physisorbed 3He. 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 model substrates: Nuclepore, and sodium. We find that the effect of the 3He depends sensitively on the particular 4He film coverage. Our most important result is that, with the addition of 3He, the third sound speed can either increase or decrease. In fact, in some regimes, the added 3He destabilizes the film and can drive “layering transitions”, leading to fairly complicated geometric structures of the film in which the outermost layer is predicted to consist of phase‐separated regions of 3He and 4He.
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