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-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_μ1/2 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≈±50  face='roman'>mT with rms flux noise S _{face='roman'>Φ, face='roman'>w}1/2≤250  face='roman'>n face='roman'>Φ₀/ face='roman'>Hz1/2 in the white noise regime and spin sensitivity S_μ1/2≤29 μ _{face='roman'>B}/ face='roman'>Hz1/2. Furthermore, we demonstrate operation in B = 0.5 T with high sensitivity in flux S _{face='roman'>Φ, face='roman'>w}1/2≈680  face='roman'>n face='roman'>Φ₀/ face='roman'>Hz1/2 and in electron spin S_μ1/2≈79 μ _{face='roman'>B}/ face='roman'>Hz1/2. We discuss strategies to further improve the nanoSQUID performance.