Possible nature of the dielectric activity of He II observed in experiments with second sound

Abstract

An attempt is made to explain the nature of the electric signal observed in He II in a second-sound standing wave. Using the general quantum-mechanical principles, we show that, due to interatomic interaction, each atom of He-II acquires a small fluctuating induced dipole moment with the average value of its modulus dat = 2eδ, δ ≃ 2.6 × 10 −4 Å. A directed flux of microscopic vortex ringswhich, together with phonons, are thermal excitations of He II -forms in the second-sound standing halfwave. This flux partially orders the chaotically oriented dipole moments of the atoms, which results in volume polarization of He II. The observed electric induction △U ≈ k B △T /2e can be explained theoretically under the assumption that each vortex ring possesses a dipole moment d vr of the order of ten atomic moments, d vr ∼ 10 dat .It is shown also that the theoretical value of the voltage △U induced in He II by the volume system of dipoles strongly depends on the dimensions of the resonator for dipoles of any origin. The experimental value of △U is the same for two resonators of different size; therefore, this voltage may be not connected with the volume polarization of He II.