Enhancement of Critical Currents and Photon Count Rates by Magnetic Field in Spiral Superconducting Nanowire Single-Photon Detectors

Abstract

We investigated the influence of magnetic fields on critical currents and photon-count rates for optical and near-infrared photons in spiral-shaped nanowire structures of different types. Nanowires with a width of about 100 nm were made in forms of square and circular spirals with a pitch of 150 nm. Magnetic field dependencies of the critical current in square spirals were asymmetric with respect to the field direction. In the current maximum, we achieved a more than 6 percent increase of the critical current. Contrary, circular spirals showed fully symmetric dependencies with the current maximum at zero magnetic field. Photon-count rates of spirals have been studied in the wavelength range from 500 to 1400 nm at magnetic fields up to 500 mT. In circular spirals, the rates of photon and dark counts were symmetric in magnetic fields at all achievable experimental conditions. In square spirals, dark and photon count rates are asymmetric with the minima occurring at opposite directions of the field. Dark count rates are lower than 10 cps at bias currents up to 90 percent of the critical value in the whole range of applied magnetic fields. Based on our results, we propose a way to decrease the minimum detectable photon flux by applying external magnetic field to the detector.