Ms. Zoharchen Sofer

Abstract:

Superconductor phase transition is characterized by a sharp drop to zero resistance at the critical temperature T_c. A different behavior –  smeared transition and a non-vanishing resistance down to a very low temperature – is observed in one-dimensional nanowires, namely wires with transverse dimensions in the order of the coherence length. Another behavior in these nanowires is the appearance of Negative MagnetoResistance (NMR), i.e., a decrease in the resistance as the external magnetic field increases. Previous works have focused on describing the effect of temperature on the NMR. In the previous dissertation we describe an exhaustive study of the effect of transport current on the NMR. We fabricated and characterized two different NbN nanowires created by using e-beam lithography. The first nanowire is amorphous with transverse dimensions of order of  the coherence length. We, therefore, refer to this wire as one dimensional (1D) nanowire. The second nanowire is granular (with a typical size of ~ 10 nm per grain) with transverse dimensions larger by factor of 5 than the coherence length. Despite the fundamental differences between these two wires, the magneto-transport measurements showed similar results for both wires.Despite the similarity between the experimental results in the behavior of R(T) and R(H), we show that different physical origins dictate the behavior in each nanowire. In the 1D nanowire the origin of these results is fluctuation in the order parameter, while in the granular wire the origin of the observed behavior stems from Josephson junctions between the grains.