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Properties of Superfluid $^4$He Films
New Phys.: Sae Mulli 2018; 68: 375~380
Published online April 30, 2018;
© 2018 New Physics: Sae Mulli.

Sang-Tack NAM*

Department of Physics and Research Institute of Natural Science, Gyeongsang National University, Jinju 52828, Korea
Correspondence to:
Received February 26, 2018; Revised March 26, 2018; Accepted March 29, 2018.
cc This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
We obtained the third-sound speed of superfluid $^4$He films on glass substrates, on polished CaF$_2$ single-crystal substrates, and on argon substrates as functions of the temperature and the film thickness by using the hydrodynamic method of Rutledge et al. We calculated the superfluid parameters $\bar{\rho}_S/\rho$ and $\bar{\rho}_Sd/T$ of the superfluid $^4$He films by using the measured third-sound speed, the van der Waals constant, and the thickness of the film. We showed that the third-sound speed and the superfluid parameters $\bar{\rho}_S/\rho$ and $\bar{\rho}_Sd/T$ for the films on argon substrates decreased as the temperature was increased at temperatures below the critical temperature when the thickness of the films was constant. Also, the third-sound speed and the parameters $\bar{\rho}_S/\rho$ and $\bar{\rho}_Sd/T$ for the films on argon substrates increased as the thickness of the films was increased when the temperatures was constant at a value below the critical temperature.
PACS numbers:, 67.25.dt
Keywords: Superfluid $^4$He films, Third-sound speed, Superfluid parameter

August 2018, 68 (8)
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