Nb nano superconducting quantum interference devices with high spin sensitivity for operation in magnetic fields up to 0.5\,T

TL;DR

This paper presents Nb-based nanoSQUIDs capable of high spin sensitivity and operation in magnetic fields up to 0.5 T, with detailed noise performance and potential for further improvements.

Contribution

The study introduces Nb nanoSQUIDs with high spin sensitivity that operate effectively in magnetic fields up to 0.5 T, demonstrating significant advancement in magnetic field resilience and sensitivity.

Findings

Operates in magnetic fields up to 0.5 T with high flux sensitivity.

Achieves spin sensitivity as low as 29 μ_B/Hz^{1/2} in intermediate fields.

Demonstrates flux noise as low as 250 nΦ_0/Hz^{1/2} in white noise regime.

Abstract

We investigate electric transport and noise properties of microstrip-type submicron direct current superconducting quantum interference devices (dc SQUIDs) based on Nb thin films and overdamped Josephson junctions with a HfTi barrier. The SQUIDs were designed for optimal spin sensitivity $S_\mu^{1/2}$ upon operation in intermediate magnetic fields $B$ (tens of mT), applied perpendicular to the substrate plane. Our so far best SQUID can be continuously operated in fields up to $B\approx\pm50\,\rm{mT}$ with rms flux noise $S_{\Phi,\rm w}^{1/2}\leq250\,\rm{n\Phi_0/Hz^{1/2}}$ in the white noise regime and spin sensitivity $S_{\mu}^{1/2}\leq29\,\rm{\mu_B/Hz^{1/2}}$. Furthermore, we demonstrate operation in $B=0.5\,\rm{T}$ with high sensitivity in flux $S_{\Phi,\rm w}^{1/2}\approx680\,\rm{n\Phi_0/Hz^{1/2}}$ and in electron spin $S_{\mu}^{1/2}\approx79\,\rm{\mu_B/Hz^{1/2}}$. We discuss strategies to further improve the nanoSQUID performance.