Reflectionless tunneling at the interface between nanoparticles and superconductors

Interfaces between disordered normal (DN) materials and superconductors (S) are known to generate conductance peaks at zero-bias voltage (V) and magnetic field (B). Using molecularly linked Au nanoparticle films as the DN component, we find that superimposed on conductance peaks are oscillations that depend simultaneously on both V and B. Such correlated conductance oscillations are predicted by a "reflectionless tunneling" phenomenon but have not been observed in other DN-S systems. Length scales extracted from periods of conductance oscillation correlate well with film nanostructure.