Imaging of Microscopic Sources of Resistive and Reactive Nonlinearities in Superconducting Microwave Devices

The technique of low-temperature laser scanning microscopy (LSM) has been applied to the investigation of local microwave properties in operating YBa₂Cu₃O₇/LaAlO₃ thin-film resonators patterned into a meandering strip transmission line. By using a modified newly developed procedure of spatially-resolved complex impedance partition, the influence of inhomogeneous current flow on the formation of nonlinear (NL) microwave response in such planar devices is analysed in terms of the independent impact from resistive and inductive components. The modified procedure developed here is dramatically faster than our previous method. The LSM capability to probe the spatial variations of two-tone, third-order intermodulation photoresponse on micron length scales is used to find the 2D distribution of the local sources of microwave NL. The results show that the dominant sources of microwave NL are strongly localized in the resistive domains.