INTERACTION OF VORTICES WITH ULTRASOUND AND THE ACOUSTIC FARADAY-EFFECT IN TYPE-II SUPERCONDUCTORS

We study the interaction of sound waves with vortices in type-II super conductors, taking into account pinning and electrodynamic forces betw een vortices and crystal displacements. We propose ultrasound techniqu es as a method for obtaining information about vortex dynamics. This i s particularly appropiate at low temperatures where transport measurem ents are ineffective. The changes in sound velocity and attenuation du e to vortices, can provide information on the elastic constants of the vortex system and on vortex dissipation, respectively. At low tempera tures the Magnus force acting on vortices leads to the acoustic Farada y effect: there is a rotation of the polarization plane of tranverse s ound waves propagating along the magnetic field. This effect is linear in the Magnus force and magnetic field in crystals with equivalent a and b axes for a field parallel to the c axis. We discuss how this eff ect can be measured by means of either pulse-echo techniques or standi ng sound waves. Also, we show that an ac electromagnetic field acting on the vortex system can generate ultrasound. We calculate the amplitu de of the generated sound waves in the linear regime and compare with recent experiments.