Excitations of superfluid 4He in porous media: Aerogel and Vycor

O. Plantevin, B. Fåk, H. R. Glyde, N. Mulders, J. Bossy, G. Coddens, and H. Schober
Phys. Rev. B 63, 224508 – Published 22 May 2001
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Abstract

We present precision neutron scattering measurements of the dynamic structure factor S(Q,ω) and the elementary excitations of liquid 4He immersed in aerogel and Vycor. In both porous media, liquid 4He supports two-dimensional (2D) layer modes at wave vectors in the roton region that propagate in the liquid layers adjacent to the media walls. The layer modes have a rotonlike energy dispersion relation with energies that are consistent with specific heat and superfluid density measurements at low temperature. Liquid 4He in these media also supports 3D phonon-roton (p-r) excitations that have energies and lifetimes at temperatures 0.5<~T<~2.3 K which are the same as in bulk liquid 4He within current precision (5μeV). The layer modes are the only new excitations observed in these disordering media to date. In Vycor, we observe a well-defined p-r excitation at temperatures above Tc in the normal phase. This suggests that there is a localized condensate (phase coherence on short length scales) above Tc in Vycor.

  • Received 20 December 2000

DOI:https://doi.org/10.1103/PhysRevB.63.224508

©2001 American Physical Society

Authors & Affiliations

O. Plantevin and B. Fåk*

  • Commissariat à l’Energie Atomique, Département de Recherche Fondamentale sur la Matière Condensée, SPSMS/MDN, 38054 Grenoble, France

H. R. Glyde and N. Mulders

  • Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716

J. Bossy

  • Centre de Recherches sur les Très Basses Températures, CNRS, BP 166, 38042 Grenoble, France

G. Coddens

  • Laboratoire Léon Brillouin, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France

H. Schober

  • Institut Laue-Langevin, BP 156, 38042 Grenoble, France

  • *Present address: ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, Great Britain.
  • Present address: Laboratoire des Solides Irradiés, Ecole Polytechnique, 91128 Palaiseau, France.
  • Present address: Physikdepartement der Technischen Universität München, Lehrstuhl E13, James Franck Str., 85748 Garching, Germany.

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Issue

Vol. 63, Iss. 22 — 1 June 2001

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