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

The vibrational modes in isotropic nonpolar dielectrics He I and He II are studied in the presence of an alternating electric field E = E(0)i(z)sin(k(0)z-omega(0)t), by solving the equations of ordinary and two-fluid hydrodynamics. There is a "coupling" between the electric field and the density fluctuations, since the density gradient leads to the spontaneous polarization P-s, and the electric force contains the term (P-s del) E. Analysis shows that the wave velocities of the first- and second-sounds propagating along E change according to the formula u(j) approximate to c(j) + chi E-j(0)2 (where j = 1, 2; c(j) is the speed of the jth sound at E-0 = 0, and chi(j) is a constant). It is found that the field E, together with the wave of the first- (second) sound (omega, k), should create in He II hybrid acoustoelectric (thermoelectric) density waves (omega + l omega(0), k + lk(0)), where l = +/- 1, +/- 2, horizontal ellipsis The amplitudes of the acoustoelectric waves and the quantity vertical bar u(1)-c(1 vertical bar) are negligibly small, but at certain omega and omega(0) they should increase resonantly. The first resonance seems to correspond to the decay of a photon into two photons with the recoil momentum being transferred to the liquid as a whole. Therefore, the electromagnetic signal spectrum should have a narrow absorption line, similar to the Mossbauer effect. Published under license by AIP Publishing.