New, Attenuated Wave Mode in He II Films
- 9 September 1966
- journal article
- research article
- Published by American Physical Society (APS) in Physical Review B
- Vol. 149 (1) , 72-76
- https://doi.org/10.1103/physrev.149.72
Abstract
It is shown that if normal-fluid motion with a viscous force is allowed in He II films, then a new wave mode is predicted by the equations of motion. The film is described here by four equations: conservation of mass, conservation of energy, the usual superfluid thermohydrodynamic equation, and the normal-fluid equation with a viscous force per unit volume. The viscosity term is , in which is the velocity of the normal fluid, is the bulk helium density, is the angular frequency of the wave, and is a dimensionless viscosity parameter. Two nontrivial wave modes are allowed: One corresponds to third sound, with a comparatively small attenuation, and the other is the new mode. Both modes are simultaneously waves in local film height, local film temperature, and superfluid and normal-fluid velocity. The new mode is heavily overdamped with an attenuation that rises from about 400 at , to about at , for waves of cps in a 250 Å film. The velocity of the mode decreases with temperature in an interesting way: The maximum velocity at 1.2°K is about 900 cm/sec, at 2.0°K about 160 cm/sec, and at 2.15°K about 60 cm/sec. It is shown that these attenuations and velocities are of the same kind as have recently been observed as anomalies in third sound. It is suggested that this new mode is generally excited along with third-sound waves and that normal fluid can move in He II films.
Keywords
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