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an elementary excitation (quasiparticle) in superfluid 4He with comparatively high energy & and momentum p. The dependence of the energy of the quasiparticles on the momentum ρ (dispersion relation) in superfluid 4He is shown in Figure 1.
I. E. Tamm suggested the name “roton” for quasiparticles with momentum close to p0 In the linear region of (p) the quasiparticles are called phonons; quasiparticles in 4He with any value of ρ are sometimes called phonons. Roton spectra have been determined with high accuracy by means of inelastic neutron scattering in superfluid 4He.
Rotons play an important role in the properties of superfluid helium at T ≳ 0.6°K. They are responsible for the existence of components of heat capacity, entropy, normal density, and other properties that vary exponentially with temperature. The kinetic properties of superfluid 4He—for example, viscosity and sound absorption—have been explained on the basis of collisions and interconversion of rotons and phonons.
REFERENCEKhalatnikov, I. M. Teoriia sverkhtekuchesti. Moscow, 1971.
M. I. KAGANOV