Abstract
We present precision neutron scattering measurements of the dynamic structure factor and the elementary excitations of liquid immersed in aerogel and Vycor. In both porous media, liquid 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 in these media also supports 3D phonon-roton (p-r) excitations that have energies and lifetimes at temperatures K which are the same as in bulk liquid within current precision 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 in the normal phase. This suggests that there is a localized condensate (phase coherence on short length scales) above in Vycor.
- Received 20 December 2000
DOI:https://doi.org/10.1103/PhysRevB.63.224508
©2001 American Physical Society