Photofluxonic detection: A new mechanism for infrared detection in superconducting thin films

Abstract

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 Φ₀=h/2e. An applied current sweeps these fluxons to opposite edges of the film, causing a voltage pulse with time‐integrated magnitude Φ₀, and leading to a time‐averaged voltage responsivity R_v = Φ₀/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.