Measurement of conduction properties of highly resistive superconducting microbridges

The authors present experimental results on the properties of very small microbridges with high junction resistance. The authors fabricated NbN microbridges with very narrow width (<100 nm) and length ( approximately 100 nm) by electron beam lithography, and measured the junction properties, such as I-V characteristics and temperature dependence. The junctions with very high resistance (>>k Omega ) exhibit unusual nonlinearity in the I-V relation, which is dual to the Josephson characteristics. The electric field effect in a two-junction array is also examined, where a gate electric field is applied to a center electrode. Experimental results agree fairly well with numerical calculations, assuming that the bridge consists of a one-dimensional array of the single-electron-tunnel junction.<>