Phonon Dispersion in Liquid Helium under Pressure

Abstract

We have studied one-phonon neutron scattering in liquid helium at a pressure of 24 atm in the range of wave-vector transfers $0.2 {\mathrm{\AA }}^{-1}<~\left|\overrightarrow{\mathrm{Q}}\right|<~0.7 {\mathrm{\AA }}^{-1}$ at $T=1.2\mathrm{}$ K. The results give a value (6.2 ± 0.6) × ${10}^{37}$ ${\mathrm{g}}^{-2\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\sec }^2$ for the parameter $\gamma$ which characterizes the phonon dispersion. The one-phonon peaks exhibit tails indicating shortened phonon life-times at elevated pressures.