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

Abstract

Keywords: bended superconducting nanostrips, current crowding, photon detection, dark counts, magnetic field asymmetry PACS number(s): 74.25. Ha, 85.25.Oj, 78.67.Uh 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.2

Magnetic-Field Enhancement of Performance of Superconducting Nanowire Single-Photon Detector

“…It has been argued that bends and turns with sharp corners are places from which dark counts mostly originate [10]. In our case, magnetic field reduces the local current density at the inner sides of bends and flattens the current density profile across bends.…”

“…The same occurs in straight strips. To overcome the reduction of the critical current at small fields, the detector layout (square spiral) with the same symmetry for all bends was proposed [10], [11]. It has been shown for square-spiral SNSPDs that magnetic field increases the critical current and PCR and decreases DCR to a minimum of less than <10 cps at the field which corresponds to the maximum of IC [11].…”

Timing jitter in photon detection by straight superconducting nanowires: Effect of magnetic field and photon flux

“…The coefficient η is the ratio of the experimental critical current to the depairing critical current at B = 0. The density of the depairing critical current is evaluated [17] according to…”

Current dependence of the hot-spot response spectrum of superconducting single-photon detectors with different layouts

“…At even larger wavelengths, mostly bends and turns contribute to the photon-count rate [16]. The transition from the plateau to the decaying part of the DE spectrum is formally described by:…”