Asymmetry in the effect of magnetic field on photon detection and dark counts in bended nanostrips

Abstract

Current crowding in the bends of superconducting nanostructures not only restricts measurable critical current in such structures, but also redistributes local probabilities for the appearance of dark and light counts. Using structures in the form of a square spiral, where all bends have the same symmetry with respect to the directions of the bias current and external magnetic field, we have shown that areas around the bends largely contribute to the rate of dark counts and to the rate of light counts at small photon energies. The minimum in the rate of dark counts reproduces the asymmetry of the maximum in the critical current as a function of the magnetic field. Contrarily, the minimum in the rate of light counts demonstrates opposite asymmetry. The rate of light counts becomes symmetric at large currents and fields. Comparison of the computed local absorption probabilities for photons and the simulated local threshold detection current reveal the areas near bends that deliver the asymmetric rate of light counts. Asymmetry in count rates is absent in circular spirals without bends.