Vibronic Effects in Superconducting Niobium Nanowires*

Research of superconducting transport through microscopic objects with intrinsic vibrational degrees of freedom is a frontier research avenue. Here we report on experimental studies of a few-atom niobium nanowires prepared in a mechanically-controlled break junction set-up. We present evidence for the resonant interaction between the ac Josephson effect and the mechanical motion of atoms in niobium dimer nanowires at frequencies up to about 8~THz. This is application-rich, but a largely unexplored frequency range (``terahertz gap''), which interrogates the lowest frequency vibrational modes of complex organic and biological molecules. We also discuss supercondicting transport and noise in niobium nanowires with oxygen contamination.