PHOTOFLUXONIC DETECTION - A NEW MECHANISM FOR INFRARED DETECTION IN SUPERCONDUCTING THIN-FILMS

A new model is proposed in which a photon of energy E = hf is absorbed by a superconducting film to create a pair of equal and opposite fluxons (or vortices), each with quantized flux PHI-O = h/2e. An applied current sweeps these fluxons to opposite edges of the film, causing a voltage pulse with time-integrated magnitude PHI-O, and leading to a time-average voltage responsivity R(v) = PHI-O/E = 1/(2ef). This is directly analogous to photoconductive detection in a semiconductor via creation of electron-hole pairs. Data on an ultrathin granular NbN film are presented which indicate a responsivity of 6000 V/W in red light, in agreement with the model. This is promising for the development of a sensitive, high-speed infrared detector using thin films of either low or high T(c) superconductors.