Effect of microwave radiation on the critical current in dirty superconductors

The current density in a dirty superconductor placed in a field of microwave radiation is calculated from Eliashberg's theory for nonequilibrium superconductivity. It is shown that the microwave-induced change in the quasiparticle distribution function Δf enhances the critical current in two ways: through a term appearing in the self-consistency equation that leads to enhancement of the order parameter; and through a change in the functional form of the supercurrent by a term related to Δf(Δ). Numerical results are presented describing the behavior of the critical current as a function of the radiation power and frequency and the temperature.