Dynamics of liquid 4He in vycor

Abstract

Using inelastic neutron scattering, we have observed well-defined phonon-roton ( p-r) excitations in superfluid 4He in Vycor over a wide wave-vector range, 0.3</=Q</=2.15 A(-1). The p-r energies and lifetimes at all temperatures are the same as in bulk liquid 4He. However, the weight of the single p-r component does not scale with the superfluid fraction rho(S)(T)/rho as it does in the bulk. In particular, we observe a p-r excitation above T(c) = 1.952 K, where rho(s)(T) = 0 in Vycor. This suggests, if the p-r excitation intensity scales with the Bose condensate, that there is a separation of the Bose-Einstein condensation temperature and the superfluid transition temperature T(c) of 4He in Vycor.