On the cause of the electrical activity of superfluid helium upon excitation of a second sound wave and normal-component velocity oscillations in it

Abstract

An explanation is proposed for a new, previously unknown effect that was recently observed experimentally: the appearance of an electric field in superfluid helium during the propagation of second sound waves or in the presence of induced oscillations of the velocity of the normal component. It is shown that the electrical potential that arises upon excitation of second sound on account of the polarization of the He atoms under acceleration because of the strong mass difference of the electrons and nuclei (the inertial effect) is proportional to the total entropy of the HeII. The analysis makes use of the idea that superfluid component of HeII is a superposition of two oppositely charged coherent Bose condensates, electronic and nuclear, coupled strongly by the Coulomb interaction. These condensates consist, respectively, of the zero-spin helium nuclei and of the strongly correlated pairs of electrons found in the singlet state and forming the completely filled 1s shell of the helium atoms. It is taken into account that, because of the interatomic interaction, the effective coherent condensate constituting the microscopic basis of the superfluid component of HeII contains intense pair and higher multiparticle condensates in addition to the “depleted” single-particle Bose–Einstein condensate. Because of this, the entropy of the superfluid quantum liquid He4 has a constant, temperature-independent contribution. It follows from the analysis that the amplitude ratio of the temperature and potential oscillations in the second sound wave, which was obtained by A. S. Rybalko, Fiz. Nizk. Temp. 30, 1321 (2004) [Low Temp. Phys. 30, 994 (2004)], can be used to determine the entropy of HeII. The appearance of electrical activity upon excitation of induced oscillations of the normal-component velocity arising as a result of torsional oscillations of the vessel containing the HeII, which was observed by A. S. Rybalko and S. P. Rubets, Fiz. Nizk. Temp. 31, 820 (2005) [Low Temp. Phys. 31, 623 (2005)], is explained qualitatively by a correction to the chemical potential quadratic in the velocity difference of the superfluid and normal components of HeII. It is shown, however, that this contribution, like the contribution due to centripetal acceleration discussed by Rybalko and Rubtsa (op. cit.), does not agree quantitatively with experiment.