Dynamics of quantum liquids in nanoporous media
Department of Physics and Astronomy, University of Delaware, Newark, Delaware, 19716, USA
We sketch our recent neutron scattering measurements of the phonon-roton (P-R) modes and Bose-Einstein condensation (BEC) of liquid 4He in porous media. The aim is to reveal the interdependence of BEC, well-defined P-R modes and superfluidity in helium confined to nanoscales and in disorder. In all porous media investigated to date, we observe well-defined P-R modes above Tc in the normal liquid phase, up to Tλ. Since well defined P-R modes are associated with BEC, this suggests that there is BEC above Tc in porous media. We interpret this as BEC localized to favorable regions separated by regions of normal fluid. At high pressures, p ≥25 bars, well defined P-R modes are no longer observed at lower wavevectors, Q ≤1.5 Å. At p ≈39 bars a roton is no longer observed. Work is in progress to explore whether loss of modes can be associated with a recently reported Quantum Phase Transition.
© EDP Sciences, Springer-Verlag, 2007