Superconductivity in single crystalline Pb nanowires contacted by normal metal electrodes

The transport properties of superconducting single crystal Pb nanowires that are 55 and 70 nm in diameter were studied by the standard four-electrode method. With normal metal electrodes, resistance-temperature and resistance-magnetic field scans show a series of resistance steps with increasing temperature and magnetic field as the wires are brought toward the normal state. The resistance-current (R-I) scans at different temperatures and magnetic fields show that the increase in R with I is punctuated with sharp steps at specific current values. A large residual resistance is observed down to 2 K. The origin of these phenomena is related to the inhomogeneity and proximity effect from the normal electrodes.