High-resolution measurements of excitations in superfluid 4He beyond the roton

High-resolution neutron inelastic scattering studies of the wavevector and temperature dependence of the excitation spectrum of 4He in the superfluid and normal-fluid phases have been made in the wavevector region ‘beyond the roton’, 2.0 < Q < 3.6 Å−1, at a pressure of 20 bar. The scattering in this region exhibits two separate components: a sharp peak at low energies and a broader continuum at higher energies. The relative intensity of these two peaks is Q-dependent. We find that the two-roton energy, 2, is never exceeded by the sharp peak at this pressure. The data are compared with the density–quasiparticle model of Glyde and Griffin and a tentative analysis of the temperature dependence of the condensate fraction n0 is made. 1