Spatially resolved observation of the critical current in high-T_c superconducting films

Abstract

The superconducting properties of high-transition-temperature (high-T_c) copper-oxide superconductors depend sensitively on their microstructure. For example, the critical current density J_c of epitaxial YBa₂Cu₃O₇ films can be several orders of magnitude higher than that of fine-grained polycrystalline films and ceramics^1,2. Local variations in the size and distribution of features such as grains, grain boundaries, anisotropy and composition play an important role in determining the superconducting properties, and also profoundly affect the normal-state properties. A technique capable of probing superconducting properties with high spatial resolution—smaller than the grain size—is thus important not only for basic understanding, but also for device and microelectronics applications. Here we combine the techniques of micro-patterning^3,4 and low-temperature scanning electron microscopy (LTSEM) ^5,6 to obtain the first spatially resolved observation of local values of the critical current I_c in high-T_c polycrystalline films. Both the range of values of I_c and the spatial distribution of the local I_c can be determined with a resolution approaching 1 (µm. This new technique can be extended easily to the spatially resolved investigation of T_c distribution, flux pinning and flux flow⁶.