  We proceed from the premise that the spectrum of elementary excitations in
the normal component in Landau's 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 one more type of elementary
excitations in superfluid helium, which we called helons. The energy spectrum
with such a 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.
