Improved design josephson junctions with hybrid nanostructured barriers

New type of Josephson junctions with hybrid nanostructured barriers has been fabricated and investigated. Heterostructures consisting of superconducting MoRe electrodes with a critical temperature about 9 K and a silicon film with a thickness of several dozens of nm (sandwiched between them) were fabricated. The silicon layer was doped by tungsten with various atomic concentrations. By using an atomic force microscope we have investigated a relief of the every layer of the fabricated Josephson junction, as a result it has been demonstrated a possibility to observe a formation of the cluster structure of tungsten in the silicon layer in the Josephson junction barrier on a nano-sized level. Measured I-V curves of these junctions demonstrate that the well-known parameter of these junctions (named the characteristic voltage) has record values. The observation is explained as the fingerprint of “open” channels in the charge transmission due to resonance-percolating trajectories inside the strongly inhomogeneous silicon interlayer with metallic nanoclusters.

I. Introduction

At present, one of the main trends in the development of superconductive electronics is the miniaturization of Josephson junctions, which requires the use of tunneling barriers with high transparency ~0.1. In [1], investigating such Nb-Al₂O₃-Nb junctions as an example, it was established that the processes of Andreev reflections play an important role in them (such as in SNS type structures) and therefore the Al₂O₃ barrier can be considered as inhomogeneous one with the universal Shep-Bauer transparency distribution [2] for the disordered interface. The universal distribution [2] has a number of drawbacks, in particular, it is not normalizable and contains the limits and , which are not realized in the experiment. The real current-voltage characteristic (CVC) is formed as a result of averaging a large number of current-voltage curves with various values of , while the values of and differ from zero and one and are determined in each concrete case by comparing experimental and calculated characteristics [3].