Amplification of electromagnetic waves excited by a chain of propagating   magnetic vortices in YBaCuO Josephson-junction arrays at 77K and above
  When a soliton propagates in a discrete lattice it excites small-amplitude linear waves in its wake. In a dc current-biased Josephson-junction (JJ) array these manifest as electromagnetic (EM) waves excited by a (magnetic field induced) chain of propagating magnetic vortices. When the vortex velocity and the phase velocity of one of the excited EM waves match, phase-locking occurs. This produces resonant steps in the current-voltage characteristics where amplification of EM radiation occurs. We report the first observation of phase-locking-induced amplification of EM radiation at 77K and above in JJ arrays made of high temperature superconductors. 
Boris Chesca, Daniel John, Christopher J. Mellor
cond-mat.supr-con