Controllable superconducting weak links

We report the experimental characteristics of controllable superconducting weak links (CLINKs), in which the necessary localized weak region is produced by creating a nonequilibrium excess quasiparticle population which suppresses the superconducting order parameter. Direct quasiparticle injection, photo-injection, and phonon injection have been used. The characteristics (e.g., critical current) of these CLINKs can be electrically or optically tuned continuously at any temperature below T
c
. The ac Josephson effect has been observed in each type. We have developed a rudimentary theory which appears to account for some of the experimental observations. The theory is based on the phenomenological Rothwarf-Taylor equations for a nonequilibrium superconductor, modified to include quasiparticle and phonon diffusion spatial dependence of the densities, together with the modified heating or T* model of Parker and existing theoretical models of weak links.