title: Anisotropic system of quasiparticles in superfluid helium.
abstract: The thermodynamic properties of anisotropic quasiparticle systems of He II are considered for all degrees of anisotropy. It is shown that the thermodynamic functions of a strongly anisotropic phonon-roton system are mainly determined by rotons at all temperatures. Analytical expressions for the roton thermodynamic functions are obtained for all degrees of anisotropy. The maximum anisotropy is limited by the criterion for thermodynamic stability, which is here derived for the whole temperature range.
authors.affiliation: Karazin Kharkov National University, Svobody Square 4, Kharkov 61077, Ukraine.
authors.forename: I N
authors.initials: IN
authors.lastname: Adamenko
authors.forename: K E
authors.initials: KE
authors.lastname: Nemchenko
authors.forename: V A
authors.initials: VA
authors.lastname: Slipko
authors.forename: A F G
authors.initials: AF
authors.lastname: Wyatt