Electromagnetic radiation from vortex flow in type-II superconductors
  We show that a moving vortex lattice, as it comes to a crystal edge, radiates into a free space the harmonics of the washboard frequency, $\omega_0=2\pi v/a$, up to a superconducting gap, $\Delta/\hbar$. Here $v$ is the velocity of the vortex lattice and $a$ is the intervortex spacing. We compute radiation power and show that this effect can be used for generation of terahertz radiation and for characterization of moving vortex lattices. 
L. N. Bulaevskii and E. M. Chudnovsky