Zero sound and atomiclike excitations: The nature of phonons and rotons in liquid 4He

We present a novel interpretation of the traditional Landau-Feynman picture of excitations in superfluid 4He. Detailed consideration of neutron-scattering data on the temperature dependence of S(Q,ω) in the region 0.4 approx-lt Q approx-lt 2 A-1 strongly suggests that while the photon is a collective zero-sound mode, the maxon roton is a strongly renormalized single-particle excitation. The condensate-induced hybridization of these two modes explains the smooth photon-maxon-roton dispersion curve as well as the vanishing intensity of the maxon-roton peak in S(Q,ω) above Tλ