RESISTIVE STATE ANOMALIES OF SUPERCONDUCTING NANOSTRUCTURES

The V(T,I,H) characteristics have been measured for various multi-prob e aluminium nanostructures. For several samples (pairs of voltage prob es) the resistance at the top of the R(T) dependence can increase the corresponding normal state value. The effect is not fully reproducible , being dependent upon the cooling history. The magnitude of the resis tance 'bump' can be reduced by a strong measuring current and/or by an external magnetic field. Two models have been proposed to explain the observed phenomena. Both models involve the existence of the N/S inte rface within the resistive transition. The inevitably formed N/S bound ary potential step gives rise to additional resistance at the interfac e. For a static model, the formation of the N/S boundary is purely det ermined by the distribution of imperfections in the sample, while for a dynamic one, the N/S interface is periodically established with the average frequency of the thermal fluctuations Gamma and relaxes during the quasiparticle relaxation time tau(Q). Both models could give the 'order of magnitude' agreement with the experiment, while the static one is simpler. The bad reproducibility of the experimental results (d ependence upon the cooling history) is attributed to the dramatic sens itivity of the mesoscopic-size samples transport properties to the dis placement of a few impurity atoms. (C) 1997 Academic Press Limited.