Proximity induced superconductivity in bulk Cu–Nb composites: The influence of interface’s structural quality

The influence of the structural quality of a normal metal–superconductor interface on the strength of the proximity effect is studied for the cylindrical geometry of bulk Cu–Nb multifilamentary composite samples. In as-drawn Cu–Nb samples the superconducting properties induced to the Cu matrix due to its proximity with Nb filaments are manifested in the magnetization measurements through a pronounced peak positioned in the low-field regime. By systematic annealing in an extended temperature regime for various durations we changed the structural quality of the Cu–Nb interfaces and as a result their transparency to the superconducting carrier. The direct comparison of scanning electron microscopy images with magnetization data revealed that the distortion of the Cu–Nb interfaces is responsible for the suppression of the proximity effect.