Volume 98, Number 5, June 2012
|Number of page(s)||6|
|Section||Condensed Matter: Structural, Mechanical and Thermal Properties|
|Published online||13 June 2012|
Phonon-roton modes in liquid 4He coincide with Bose-Einstein condensation
Institut Néel, CNRS-UJF - BP 166, F-38042 Grenoble Cedex 9, France, EU
2 Institut Laue-Langevin - BP 156, F-38042 Grenoble, France, EU
3 Université Joseph Fourier, UFR de Physique - F-38041 Grenoble Cedex 9, France, EU
4 Department of Physics and Astronomy, University of Delaware - Newark, DE 19716-2593, USA
Accepted: 15 May 2012
We present neutron scattering measurements of the phonon-roton (P-R) and layer modes of liquid 4He confined in MCM-41 under pressure up to 38 bar. The data shows unambiguously that the P-R mode exists at low temperature only. As temperature is increased, there is a gradual transfer of intensity from the P-R mode to the normal liquid response, which lies at a lower energy at higher pressure. The transfer takes place with no observable mode broadening. The loss of P-R modes is identified with the loss of Bose-Einstein condensation (BEC). The mode giving rise to the specific heat, cV, of liquid 4He in porous media (e.g., gelsil) at higher temperature is the layer mode since the energy of the mode extracted from cV and the layer mode energy are the same.
PACS: 61.05.fg – Neutron scattering (including small-angle scattering) / 67.10.Ba – Boson degeneracy / 67.25.dr – Restricted geometries
© EPLA, 2012
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