Intrinsic detection efficiency of superconducting single photon detector in the modified hot spot model

TL;DR

This paper provides a theoretical analysis of how the intrinsic detection efficiency of superconducting single photon detectors depends on current and magnetic field, highlighting the effects of hot spot position and vortex dynamics.

Contribution

It introduces a modified hot spot model to explain the smooth and sharp dependencies of IDE on current, incorporating the effects of magnetic fields and vortex entry mechanisms.

Findings

IDE depends on hot spot position relative to film edges.

Weak magnetic fields significantly influence IDE when vortex entry is fluctuation-assisted.

Different vortex entry mechanisms lead to distinct IDE current dependence behaviors.

Abstract

We theoretically study the dependence of the intrinsic detection efficiency (IDE) of superconducting single photon detector on the applied current $I$ and magnetic field $H$. We find that the current, at which the resistive state appears in the superconducting film, depends on the position of the hot spot (region with suppressed superconductivity around the place where the photon has been absorbed) with respect to the edges of the film. It provides inevitable smooth dependence IDE(I) when IDE $\sim 0.05-1$ even for homogenous straight superconducting film and in the absence of fluctuations. When IDE $\lesssim 0.05$ much sharper current dependence comes from the fluctuation assisted vortex entry to the hot spot located near the edge of the film. We find that weak magnetic field strongly affects IDE when the photon detection is connected with fluctuation assisted vortex entry (IDE$\ll 1$) and it weakly affects IDE when the photon detection is connected with the current induced vortex entry to the hot spot or nucleation of the vortex-antivortex pair inside the hot spot (IDE$\sim 0.05-1$).