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

TL;DR

This study investigates how magnetic fields asymmetrically influence photon detection and dark counts in superconducting nanostrips with bends, revealing that current crowding affects local detection probabilities and critical current asymmetries.

Contribution

It demonstrates that bends in superconducting nanostrips cause asymmetric dark and light counts under magnetic fields, highlighting the role of current crowding in detection behavior.

Findings

Dark counts are concentrated around bends and show magnetic field asymmetry.

Light counts originate near bends and exhibit opposite asymmetry to dark counts.

Symmetry in light counts appears at high currents and magnetic fields.

Abstract

Current crowding in the bends of superconducting nano-structures not only restricts measurable critical current in such structures but also redistributes local probabilities for dark and light counts to appear. Using structures from strips in the form of a square spiral which contain bends with the very same curvature with respect to the directions of bias current and external magnetic field, we have shown that dark counts as well as light counts at small photon energies originate from areas around the bends. The minimum in the rate of dark counts reproduces the asymmetry of the maximum critical current density as function of the magnetic field. Contrary, the minimum in the rate of light counts demonstrate opposite asymmetry. The rate of light counts become symmetric at large currents and fields. Comparing locally computed absorption probabilities for photons and the simulated threshold detection current we found the approximate locations of areas near bends which deliver asymmetric light counts. Any asymmetry is absent in Archimedean spiral structures without bends.