Excitations of superfluid {sup 4}He in porous media: Aerogel and Vycor
We present precision neutron scattering measurements of the dynamic structure factor S(Q,{omega}) and the elementary excitations of liquid {sup 4}He immersed in aerogel and Vycor. In both porous media, liquid {sup 4}He 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 {sup 4}He in these media also supports 3D phonon-roton (p-r) excitations that have energies and lifetimes at temperatures 0.5{le}T{le}2.3 K which are the same as in bulk liquid {sup 4}He within current precision (5{mu}eV). 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 T{sub c} in the normal phase. This suggests that there is a localized condensate (phase coherence on short length scales) above T{sub c} in Vycor.
- Sponsoring Organization:
- (US)
- OSTI ID:
- 40203504
- Journal Information:
- Physical Review B, Vol. 63, Issue 22; Other Information: DOI: 10.1103/PhysRevB.63.224508; Othernumber: PRBMDO000063000022224508000001; 046122PRB; PBD: 1 Jun 2001; ISSN 0163-1829
- Publisher:
- The American Physical Society
- Country of Publication:
- United States
- Language:
- English
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