STSM of Simon Collienne at Néel Institut (Grenoble): Transport properties of Nb-based multiterminals tuned by electroannealing

The fabrication of SNS junctions involves delicate lithography, as nanoscale conductors of different materials have to be connected via perfectly clean interfaces. While simple metallic SNS junctions are routinely fabricated using the shadow-evaporation technique, using this technique becomes very cumbersome for multi-terminal junctions. We have recently discovered that controlled electroannealing of monolithic Nb constrictions, can lead to a structural and chemical transformation of the constriction and thus locally deplete the superconducting properties. First measurements, realized at temperatures above 2 K, indicate that in a Nb tri-junction, the central node can be electroannealed to form a Josephson junction. The aim of the present STSM was to complement these measurements, in order to provide a more complete understanding of the nature of the Josephson junctions formed by electroannealing at lower temperatures. The effort was devoted to the measurement of voltage maps (V maps) at 100 mK as a function of two imposed currents whose derivatives (dV/dI maps) describe the transport dynamics of the multiterminal. Partial results from this STSM were published in March 2022 in Nanoscale, 2022,14, 5425-5429