Criterion of superfluidity, elementary excitations, and heat capacity singularity in superfluid helium

We proceed from the premise that the spectrum of elementary excitations in the normal component in the Landau theory of superfluidity should depend on the superfluid helium temperature. This leads to generalization of the Landau superfluidity criterion. On this basis, taking into account available experimental data on inelastic neutron scattering, it is shown that, in addition to phonon-roton excitations, there is another type of elementary excitation in superfluid helium, which we called helons. The energy spectrum with such momentum dependence was first proposed by Landau. The helon energy spectrum shape and its temperature dependence make it possible to explain the singular behavior of the heat capacity of superfluid helium near its phase transition to the normal state.