Magnus force and acoustic Stewart-Tolman effect in type-II superconductors

We present an acoustic method for the study of the effective Magnus force in type-II superconductors. The method is based on the measurement of the amplitude and the phase of the electromagnetic field radiated by a superconductor due to vortex oscillations excited by a transverse elastic wave. The method does not require the flux flow regime and allows us to measure the Magnus force almost everywhere over the range of the existence of the mixed state. We have measured the field dependence of the Magnus force in nonmagnetic borocarbides (electron-type conductors) and in Nb (hole-type conductor). It is found that in borocarbides the sign of the Magnus force in the mixed state has the same sign as the Lorentz force acting on charge carriers in the normal state, and its value (counted per one vortex of unit length) has only a weak dependence on the magnetic field. In Nb the gyroscopic force changes its sign under transition from the normal to the mixed state. The essential point of the method is the registration of the electromagnetic radiation from the superconductor at zero magnetic field caused by the acoustic Stewart-Tolman effect.