Spatial distribution analyses of superconducting transition temperature in epitaxial YBa₂Cu₃O₇ film using variable temperature scanning laser microscopy

The spatial distribution of superconducting properties using variable temperature scanning laser microscope (VTSLM) has been investigated. The superconducting thin film used in this study is an epitaxial YBa₂Cu₃O₇ film photolithographically patterned to a 300 μm-wide bridge. Since the voltage response, δV(x, y) is proportional to dR/dT(x, y), the spatial distribution of superconducting transition can be obtained in VTSLM images. In the resistive transition region, there is a strong correlation between the VTSLM images and the resistance of the sample. With decreasing resistance, the area with large δV(x, y) shifts toward the ends of the bridge. This indicates that the resistive transition is not uniform and both ends of the bridge have lower transition temperature, T_c. Different currents or different output power of lasers do not affect the images. VTSLM technique is a powerful tool to image the local superconducting properties and to identify the weaker superconducting areas.