ZERO SOUND AND ATOMIC-LIKE EXCITATIONS - THE NATURE OF PHONONS AND ROTONS IN LIQUID-HE-4

We present a novel interpretation of the traditional Landau-Feynman picture of excitations in superfluid He4. Detailed consideration of neutron-scattering data on the temperature dependence of S(Q,) in the region 0.4Q2 AIS 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,) above. © 1990 The American Physical Society.