Vortex assisted mechanism of photon counting in superconducting nanowire single photon detector revealed by external magnetic field

TL;DR

This study investigates the photon detection mechanism in superconducting nanowire single photon detectors using an external magnetic field, revealing that vortex hot spot models better explain the observed behaviors than hot belt models.

Contribution

The paper demonstrates that vortex hot spot models, considering vortex dynamics, more accurately explain the detection mechanism than traditional hot belt models.

Findings

Weak magnetic field dependence of PCR for 450 nm photons supports vortex hot spot model.

PCR decreases with magnetic field for wavelengths 450-1200 nm, explained by vortex pinning.

Vortex dynamics are crucial for understanding photon detection in superconducting nanowires.

Abstract

We use external magnetic field to probe the detection mechanism of superconducting nanowire single photon detector. We argue that the hot belt model (which assumes partial suppression of the superconducting order parameter $\Delta$ across the whole width of the superconducting nanowire after absorption of the single photon) does not explain observed weak field dependence of the photon count rate (PCR) for photons with $\lambda$=450 nm and noticeable {\it decrease} of PCR (with increasing the magnetic field) in some range of the currents for photons with wavelengths $\lambda$ =450-1200 nm. Found experimental results for all studied wavelengths $\lambda = 450-1550$ nm could be explained by the vortex hot spot model (which assumes partial suppression of $\Delta$ in the area with size smaller than the width of the nanowire) if one takes into account nucleation and entrance of the vortices to the photon induced hot spot and their pinning by the hot spot with relatively large size and strongly suppressed $\Delta$.