Temperature Dependence of Critical Current Fluctuations in Nb/AlO$\mathrm{_{x}}$/Nb Josephson Junctions

TL;DR

This study investigates the low-frequency critical current noise in Nb/AlO$_{ ext{x}}$/Nb Josephson junctions, revealing a 1/f spectral density that scales inversely with junction area and decreases linearly with temperature from 4.2 K to 0.46 K.

Contribution

It provides detailed measurements of critical current noise in Nb/AlO$_{ ext{x}}$/Nb junctions, showing independence from critical current density and temperature-dependent noise reduction.

Findings

Critical current noise spectral density scales as 1/f and inversely with area.

Noise level is approximately 2.0 x 10^{-12} /Hz at 1 Hz for 1 μm^2 junctions.

Critical current noise decreases linearly with temperature from 4.2 K to 0.46 K.

Abstract

We have measured the low frequency critical current noise in Nb/AlO$_{\mathrm{x}}$/Nb Josephson junctions. Unshunted junctions biased above the gap voltage and resistively shunted junctions biased near the critical current, $I_{c}$, have been measured. For both, the spectral density of $\delta I_{c}/I_{c}$, $S_{i_{c}}(f)$, is proportional to $1/f$, scales inversely as the area, $A$, and is independent of $J_{c} \equiv I_{c}/A$ over a factor of nearly 20 in $J_{c}$. For all devices measured at 4.2 K, $S_{i_{c}}$(1 Hz)$= 2.0 \pm 0.4 \cdot 10^{-12}$/Hz when scaled to A=1 $\mu$m$^{2}$. We find that, from 4.2 K to 0.46 K, $S_{i_{c}}(f)$ decreases linearly with temperature.