Transition radiation of moving Abrikosov vortices

We predict that Abrikosov vortices moving towards the surface of a superconductor emit electromagnetic radiation into free space. Passage of a single vortex line traveling at constant speed $\mathbf{v}$ from a superconducting half space, $x<\mathrm{}0,$ towards the vacuum half space, $x>\mathrm{}0,$ is discussed in detail. The frequency distribution of the radiated intensity displays a pronounced maximum at microwave frequencies around $\omega \simeq |v_x|/\lambda ,$ where $\lambda$ is the magnetic penetration depth. Coherent motion of a lattice of flux lines leads to constructive interference and increases the strength of the radiated power per vortex line by a large factor. Also the radiation source may be used to measure the velocity of Abrikosov vortices and to determine the magnetic penetration depth.