Structural and transport properties of Nb nanowires

High-resolution conductance measurements in niobium nanowires below the superconducting transition temperature are presented. Results are shown for a complete multistage elongation-compression cycle of a nanoscale contact. We focus on a bistability region which manifests itself as random telegraph noise. Density functional structural optimizations and conductance calculations using the non-equilibrium Green’s functions method reproduce and explain the measurements. In particular, the observed bistability is associated with formation of a niobium dimer between the opposing electrodes, with the dimer shuttling between a symmetric, high conductance, and an asymmetric, low conductance, configurations in the gap.