Effect of hydrogen molecules on the electronic transport through atomic-sized metallic junctions in the superconducting state

Abstract

In this paper the interaction of hydrogen molecules with atomic-sized superconducting nanojunctions is studied. It is demonstrated by conductance histogram measurements that the superconductors niobium, tantalum, and aluminum show a strong interaction with hydrogen, whereas for lead a slight interaction is observed and for tin and indium no significant interaction is detectable. For Nb, Ta, and Pb the subgap method is applied to determine the transmission eigenvalues of the nanojunctions in hydrogen environment. It is shown that the behavior of Nb and Ta nanojunctions is strongly modified by hydrogen molecules as reflected by the pronounced changes in the conductance histogram, the appearance of extremely long conductance traces, and the observation of negative differential conductance phenomenon in the $dI/dV$ curve. Surprisingly the transport properties based on the measured transmission eigenvalues are similar to those of pure junctions. Our results imply that in Nb and Ta the interaction with hydrogen causes a plastic, ductile behavior and the formation of long nanoscale necks, but no well-defined single-molecule contacts are formed, and the transport properties are still dominated by Nb and Ta.