Acoustic modes in He I and He II in the presence of an alternating electric field

Abstract

By solving the equations of ordinary and two-fluid hydrodynamics, we study the oscillatory modes in isotropic nonpolar dielectrics He I and He II in the presence of an alternating electric field $\text{E}=E_0{\text{i}}_z\sin (k_{0}z-{\omega }_{0}t)$. The electric field and oscillations of the density become ``coupled,'' since the density gradient causes a spontaneous polarization ${\text{P}}_s$, and the electric force contains the term $({\text{P}}_s\nabla )\text{E}$. The analysis shows that the field $\text{E}$ changes the velocities of first and second sounds, propagating along $\text{E}$, by the formula $u_j\approx c_j+{\chi }_j{E}_0^2$ (where $j=1,2$; $c_j$ is the velocity of the $j$-th sound for $E_0=0$, and ${\chi }_j$ is a constant). We have found that the field $\text{E}$ jointly with a wave of the first (second) sound $(\omega ,k)$ should create in He II hybrid acousto-electric (thermo-electric) density waves $(\omega +l{\omega }_0,k+l{k}_0)$, where $l=\pm 1,\pm 2,\dots$. The amplitudes of acousto-electric waves and the quantity $|u_1-c_1|$ are negligibly small, but they should increase in the resonance way at definite $\omega$ and ${\omega }_0$. Apparently, the first resonance corresponds to the decay of a photon into two phonons with the transfer of a momentum to the whole liquid. Therefore, the spectrum of an electromagnetic signal should contain a narrow absorption line like that in the Mössbauer effect.

23 pages, 1 figure; v3: accepted version

References in corpus (5)

• Size effects and depolarization field influence on the phase diagrams of cylindrical ferroelectric nanoparticles
• To the theory of the electric activity of He II induced by waves of first and second sounds
• Low-lying energy levels of a one-dimensional weakly interacting Bose gas under zero boundary conditions
• On the effect of superfluid flows on the interaction of microwaves with He II
• Electric field and electric forces in a spontaneously polarized nonpolar isotropic dielectric