Characterization of Scanning SQUID Probes Based on 3D Nano-Bridge Junctions in Magnetic Field**Supported by the National Key R &D Program of China (Grant Nos. 2017YFF0206105, 2016YFA0301002 and 2017YFA0303000), the Young Investigator Program of CAS (Grant No. 2016217), the Frontier Science Key Programs of the CAS (Grant No. QYZDYSSW-JSC033), and the Strategic Priority Research Program of CAS (Grant No. XDA18000000), the

Abstract

We develop superconducting quantum interference device (SQUID) probes based on 3D nano-bridge junctions for the scanning SQUID microscopy. The use of these nano-bridge junctions enables imaging in the presence of a high magnetic field. Conventionally, a superconducting ground layer has been employed for better magnetic shielding. In our study, we prepare a number of scanning SQUID probes with and without a ground layer to evaluate their performance in external magnetic fields. The devices show the improved magnetic modulation up to 1.4 T. It is found that the ground layer reduces the inductance, and increases the modulation depth and symmetricity of the gradiometer design in the absence of the field. However, the layer is not compatible with the use of the scanning SQUID probe in the field because it decreases its working field range. Moreover, by adding the layer, the mutual inductance between the feedback coil and the SQUID also decreases linearly as a function of the field.