Energy spectrum of impurity excitations in superfluid helium
Abstract
The experimental data on the density of the normal component in helium-isotope solutions have been used to examine the form of the Fermi branch in the elementary-excitation spectrum. It has been found that the state density for the impurity excitations of large momentum is higher than had previously been assumed, and also that these quasiparticles produce an appreciable contribution to the thermodynamic parameters. The dispersion law obtained allows one to describe with good accuracy the available experimental data on the normal density for 3He-4He solutions over wide ranges of temperatures and concentrations. It has been found that the energy spectrum of the 3He quasiparticles has a new feature—an end point, at which an impurity excitation decays into a roton and a 3He quasiparticle of small momentum.