Quantitative Magneto-Optical Imaging of Supercurrents in Heavy-Ion Irradiated Cuprate and Pnictide Superconductors

Spatial distributions of magnetic field and of current density in superconductors are obtained, in real-time, by the magneto-optical imaging technique with an indicator film. Quantitative values of the local magnetic field and then of the local current density were achieved by a careful optical calibration and custom algorithms for the inversion of Biot-Savart law. An iterative procedure was developed for the correction of artifacts due to the coupling of the indicator film magnetization with the in-plane magnetic field generated by the superconducting sample. This technique is highly valuable when the sample under study has nonuniform properties. Several cases of such systems are shown. Particular attention is devoted to the local variation of structural and chemical properties by means of heavy-ion irradiation. A comparative study of swift-ion irradiation effects between cuprate and pnictide superconductors is addressed. For the case of cuprate materials, some successful applications of the heavy ion irradiation engineering are presented and discussed.