Amplification of ultrasonic waves by a moving vortex structure

Abstract

The interaction of a longitudinal ultrasonic wave with a moving vortex structure is considered for high-T c superconductors. It is found that this interaction contributes to the attenuation coefficient and the velocity of this wave. Expressions relating these contributions to the vortex structure velocity are derived. As the velocity of the vortex structure exceeds the wave velocity, the contribution to the attenuation coefficient is found to change its sign, and, hence, the wave can be amplified. This effect can be observed relatively easy in a periodic superconducting film structure when the electric current is passed through the film in the presence of the surface acoustic waves. Values of the current required to observe the amplification are estimated for selected ultrasonic frequencies.