Mesoscopic Superconducting–Normal Metal–Superconducting Transistor

In a mesoscopic superconductor–normal metal–superconductor ( $\mathrm{SNS}$) heterostructure the quasiparticle distribution can be driven far from equilibrium by a voltage applied across the normal metal. This reduces the supercurrent between the superconducting electrodes, which creates the possibility of using these $\mathrm{SNS}$ junctions as fast switches and transistors. We describe the system in the framework of the quasiclassical theory and find good agreement with recent experiments. We propose further experimental tests, for instance, the voltage dependence of the current-phase relation, which includes a transition to a $\pi$ junction.