Dynamics of quantum liquids in nanoporous media

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 T_c in the normal liquid phase, up to T_λ. Since well defined P-R modes are associated with BEC, this suggests that there is BEC above T_c 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 ?. 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.