Neutron scattering by rotons in liquid helium

摘要: The elementary excitations in superfluid helium have been studied the wave-vector range $1.5lQl2.3$ ${\mathrm{\AA{}}}^{\ensuremath{-}1}$ by inelastic neutron scattering. single-excitation scattering function ${\mathcal{S}}_{1} (Q, \ensuremath{\hbar}\ensuremath{\omega})$ was measured for pressures between 1 atm and solidification pressure temperatures from 1.3\ifmmode^\circ\else\textdegree\fi{}K to above transition temperature ${T}_{\ensuremath{\lambda}}$. dispersion curves were fitted parabolas appropriate Landau parameters tabulated vs pressure. By accounting effect of instrumental resolution it possible observe a line broadening at low which sets when slope curve equals sound velocity. There are strong indications that this is due roton-phonon interaction proposed Pitaevskii. observed approaches ${T}_{\ensuremath{\lambda}}$ well accounted roton-roton as calculated Khalatnikov. results related through thermodynamics other properties liquid spectral form compared those magnetic systems close critical temperature.