On possibility of two phase transitions in liquid helium
Institute for Theoretical Physics, National Science Center "Kharkov Institute of Physics and Technology", National Academy of Sciences of Ukraine, 1 Akademicheskaja Str., Kharkov 61108, Ukraine
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine 47 Lenin Ave., Kharkov 61103, Ukraine
Received March 19, 2013
An explanation for the nature of dielectric permittivity and density maxima, observed in liquid helium above the temperature of superfluid transition, is proposed. It is shown, that their existence is probably due to a phase transition, which results in a spontaneous polarization. The possibility of this transition in the liquid is related to the fact that polarization lowers energy levels of an atom, thus the polarization appears energy-optimal, especially for light atoms. At the same time the appearance of an electric dipole moment gives in rise to an additional electric field and, therefore, increases the energy. Consequently, the possibility of spontaneous polarization of atomic system is determined by the competition of the given factors. Thus, acorrding to the notions developed, as the temperature decreased there occurs liquid helium in the transition to a polarized normal phase, and only then there occurs a superfluids transition from nonzero polarisation state. The transition of normal liquid to a polarized phase is described in terms of the phenomenological theory of phase transitions. It is shown, that the transition can be either of the first or the second order.
PACS: 31.15.ap Polarizabilities and other atomic and molecular properties; PACS: 67.25.–k 4He; PACS: 64.70.–p Specific phase transitions; PACS: 77.22.–d Dielectric properties of solids and liquids.