Photon detection by current-carrying superconducting film: A time-dependent Ginzburg-Landau approach

Abstract: We study dynamics of the order parameter in a superconducting film with transport current after absorption of a single photon. The system from the time-dependent Ginszburg-Landau equation, Poisson's equation for an electrical potential and the heat diffusion equation was solved numerically. For each photon energy in the absence of fluctuations, there exists a corresponding threshold current below which the superconducting state is stable and no voltage appears between the ends of the film. At larger currents the superconducting state collapses starting from the appearance of a vortex-antivortex pair in the center of the region with suppressed superconducting order parameter which has been created by the absorbed photon. Lorentz force causes motion of these vortices that heats the film locally and gives rise to a normal domain. When biased with the fixed current, the film latches in the normal state. In the regime when current via superconductor may change, which is more relevant for experiments, the normal domain exists only for a short time resulting in the voltage pulse with the duration controlled by the kinetic inductance of the superconducting film.