Noise current induced electrical transport anomalies near the superconducting transition in mesoscopic aluminum lines

We investigate whether unintentionally applied currents may have induced the previously reported resistive and current-voltage characteristic anomalies near the superconducting transition temperature in quasi-one-dimensional aluminum lines. Our samples show no intrinsic anomalies, but a low frequency current deliberately added to the ordinary measuring current induces a resistive peak near the transition. Additional a.c. current applied to the voltage leads instead of the current leads induces an excess voltage peak near the critical current in V(I) curves. The resistive peak near the transition results from mixing, but we cannot explain the voltage peak by a simple mixing analysis. The similarity of the resistive and V(I) peaks to previous observations suggests possible extrinsic effects in earlier work.