Scanning SQUID study of ferromagnetism and superconductivity in infinite-layer nickelates

This work studied superconductivity and magnetism in infinite-layer nickelate films with scanning SQUID and cross-sectional STEM. The authors found a landscape of superparamagnetism from NiOx nanoparticles that are extrinsic to the superconductivity. They imaged superconducting vortices and determined the penetration depth. They measured the local diamagnetism, finding a consistent value of the penetration depth. The superfluid density exhibits nearly T-linear dependence, suggesting possible $d$-wave superconductivity. Using scanning SQUID to image the various sources of magnetism in superconducting nickelates paves the way for further studies of vortex dynamics and flux quantization in these recently discovered superconductors.