Phonon mediated helium atom transmission through superfluid helium four

• Published in: Journal of low temperature physics Vol. 140; no. 5-6; pp. 429 - 449
• Main Authors: LIDKE, K. A, WYNVEEN, A, BAISCH, N, KOAY, C, GIESE, C. F, HALLEY, J. W
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer 01.09.2005
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Films (including physical adsorption); Physics; Quantum fluids and solids; liquid and solid helium; Thin films; Thickness; Wave transmission; Translational energy; Rotons; Ripplons; Liquid vapor interface; Phonons; Superfluid; Bolometers; Liquid films
• ISSN: 0022-2291; 1573-7357
• DOI: 10.1007/s10909-005-7325-2

We report results of experiments in which pulses of helium vapor with translational energies of 3 K are directed at a thin film of' superfluid helium at a temperature of about 0.2 K suspended over a cesium covered orifice in a platinum film. The response of the superfluid film was detected by a superconducting titanium bolometer placed on the side of the film opposite to that of the source. For films of approximately 1 mm in thickness we find no response of the bolometer within the limits of our detector. However, for films of less than 100 p, thickness, we find a response which is of the same temporal shape, but smaller in amplitude, than that of the orifice when it is not covered with superfluid helium. We interpret these results to mean that we are seeing phonon mediated transmission in the thin films. Roton and condensate mediated transmission amplitudes for these conditions are apparently too small for us to detect in any of the films. This result is consistent with the theoretical results of Sobnack and Inkson [M. B. Sobnack, C. Inkson, and J. C. H. Fung, Phys. Rev. B 60, 3465 (1999)] concerning the amplitude of proton to atom and photon to atom conversion as a function of the atomic energy.