Abstract
We attribute the formation of a shoulder in the high-frequency ultrasonic attenuation in superfluid helium under pressure to a restriction on the three-phonon process with thermal phonons. The restriction is proposed to follow from the pressure dependence of the phonon dispersion at zero temperature. The steep rise above the shoulder due to phonon-roton and roton-roton interactions also indicates large dispersion effects under pressure.
- Received 22 July 1971
DOI:https://doi.org/10.1103/PhysRevLett.27.654
©1971 American Physical Society