Nonstationary state of superconductors: Application to nonequilibrium tunneling detectors

The nonequilibrium state of a superconductor caused by an external source (e.g., x or {gamma} rays) and its relaxation dynamics are studied. Microscopic theory allows one to evaluate the distribution functions and characteristic time scales for all cascade stages. The appearance of quasiparticles in the nonequilibrium state leads to an additional contribution to the tunneling current. The time dependence of the current flowing through a superconducting tunneling detector is evaluated. {copyright} {ital 1998} {ital The American Physical Society}