Probing inhomogeneous superconductivity and magnetism in complex oxide heterostructures with scanning SQUID

Complex oxide heterostructures offer unique opportunities for engineering electronic and magnetic systems, combining functionalities of their constituent materials and, in some cases, exhibiting emergent properties. The reduced dimensionality and broken inversion symmetry at interfaces can make them particularly sensitive to local variation in the crystal lattice. A key problem is to disentangle the intrinsic properties of heterostructures from those of ordered states stabilized by defects or other sources of inhomogeneity. I will discuss two studies which used scanning superconducting quantum interference device (SQUID) microscopy, a local magnetic probe, to investigate the effects of intrinsic or controlled inhomogeneity in complex oxide heterostructures. In the first, we imaged superconductivity in lanthanum aluminate/strontium titanate (LAO/STO) and delta-doped STO heterostructures. Spatial motifs in our measurements demonstrate that different orientations of structural domains with respect to the symmetry-breaking interface result in different superconducting transition temperatures. While LAO and STO are both nonmagnetic in the bulk, many experimental probes have found signatures of magnetism in LAO/STO heterostructures, with local measurements showing that magnetism, when present, is inhomogeneous. In our second study, we investigated oxygen vacancies as a proposed mechanism for the magnetism by measuring samples with differing oxygen content, placing tight limits on magnetism, even in the most strongly reduced samples.