Magnetic signature of granular superconductivity in electrodeposited Pb nanowires

Nanocrystalline freestanding Pb nanowires ∼200nm in diameter were fabricated by electrodeposition into track etched polycarbonate membranes in order to study their superconducting properties. Their superconducting critical temperature, as determined by measuring the Meissner effect, was the same as for bulk Pb, but their critical field was greatly enhanced up to ∼3000Oe. By assuming the wires consisted of spherical superconducting grains, an estimated grain size r=60±25nm was obtained from the magnetization measured as a function of the applied magnetic field at a fixed temperature. An independent estimate for r=47±12nm, in good agreement with the previous one, was obtained from the magnetization measured as a function of temperature at a fixed applied magnetic field. Transmission electron microscopy was used to characterize grain size at the wire edges, where a grain size in agreement with the magnetic studies was observed.