# Determining the depairing current in superconducting nanowire single-photon detectors

## TL;DR

This paper presents a method to estimate the depairing current in superconducting nanowire single-photon detectors by analyzing the bias current dependence of their kinetic inductance through resonance frequency shifts.

## Contribution

It introduces a technique using resonance frequency measurements to directly determine the depairing current, validated by the fast relaxation model, aiding in nanowire quality assessment.

## Key findings

- Fast relaxation model accurately fits experimental data
- Resonance frequency shifts correlate with kinetic inductance changes
- Method enables direct measurement of depairing current

## Abstract

We estimate the depairing current of superconducting nanowire single photon detectors (SNSPDs) by studying the dependence of the nanowires kinetic inductance on their bias current. The kinetic inductance is determined by measuring the resonance frequency of resonator style nanowire coplanar waveguides both in transmission and reflection configurations. Bias current dependent shifts in the measured resonant frequency correspond to the change in the kinetic inductance, which can be compared with theoretical predictions. We demonstrate that the fast relaxation model described in the literature accurately matches our experimental data and provides a valuable tool for direct determination of the depairing current. Accurate and direct measurement of the depairing current is critical for nanowire quality analysis, as well as modeling efforts aimed at understanding the detection mechanism in SNSPDs.