Amplification of longitudinal ultrasonic waves by a moving vortex structure in type II superconductors

A moving vortex structure can amplify (generate) longitudinal acoustic waves when the velocity of its motion exceeds a certain critical velocity. The critical velocity is determined by the logarithmic derivative of the viscosity coefficient of the vortex structure with respect to the magnetic field and may be much smaller than the speed of sound. In particular, this effect suggests an alternative explanation for the plateau observed in the current-voltage characteristic of superconducting bridges in a perpendicular magnetic field [S.G. Doettinger et al., Phys. Rev. Lett. 73, 1691 (1994)].