Phonon Dispersion Measurements on a hcpHe4Single Crystal at 27 atm

Abstract

Phonon dispersion relations along $\left[10\mathrm{}\overline{1}0\right]$ in the hcp phase of ${\mathrm{He}}^4$ have been determined by triple-axis neutron spectrometry. Optical as well as acoustic branches were observed at 27 atm and 0.99°K in a single crystal grown from the superfluid phase.