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

摘要

We investigate electric transport and noise properties of microstrip-typesubmicron direct current superconducting quantum interference devices (dcSQUIDs) based on Nb thin films and overdamped Josephson junctions with a HfTibarrier. The SQUIDs were designed for optimal spin sensitivity $S_\mu^{1/2}$upon operation in intermediate magnetic fields $B$ (tens of mT), appliedperpendicular to the substrate plane. Our so far best SQUID can be continuouslyoperated 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 regimeand 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 furtherimprove the nanoSQUID performance.