Resistive-state anomaly in superconducting nanostructures

The resistive anomaly, an increase of sample resistance above the normal st ate value at the top of the superconducting transition, has been studied ex perimentally in various aluminum nanostructures. The effect is not absolute ly reproducible being dependent on the cooling history and on the particula r arrangement of voltage and current probes for multiterminal samples. If t he anomaly is clearly observed, its magnitude can be suppressed by a strong bias current and/or magnetic field. It is shown that the main factor deter mining the form of the R(T) transition in lift-off fabricated nanostructure s is the inevitable film inhomogeneity, being a "fingerprint" of each parti cular sample. The origin of the anomaly is attributed to a superposition of two processes. First, the formation of deformed (not perpendicular to the wire axis) N/S boundaries, and, second, the existence of a nonequilibrium r egion inside the superconducting domain close to this N/S interface, charac terized by a finite value of the electric field and the corresponding effec tive resistance. Only a combination of the above effects can give a reasona ble quantitative agreement with experimental data. [S0163-1829(99)02506-0].