Universality of transport properties of ultra-thin oxide films

Abstract

We report low-temperature measurements of current-voltage characteristics for highly conductive Nb/Al-AlOx-Nb junctions with thicknesses of the Al interlayer ranging from 40 to 150 nm and ultra-thin barriers formed by diffusive oxidation of the Al surface. In the superconducting state these devices have revealed a strong subgap current leakage. Analyzing Cooper-pair and quasiparticle currents across the devices, we conclude that the strong suppression of the subgap resistance comparing with conventional tunnel junctions originates from a universal bimodal distribution of transparencies across the Al-oxide barrier proposed earlier by Schep and Bauer. We suggest a simple physical explanation of its source in the nanometer-thick oxide films relating it to strong local barrier-height fluctuations which are generated by oxygen vacancies in thin aluminum oxide tunnel barriers formed by thermal oxidation.

revised text and a new figure

References in corpus (4)

• Are pinholes the cause of excess current in superconducting tunnel junctions? A study of Andreev current in highly resistive junctions
• Control of defect-mediated tunneling barrier heights in ultrathin MgO films
• Reduction of low-frequency 1/f noise in Al-AlOx-Al tunnel junctions by thermal annealing
• Subgap conductivity in SIN-junctions of high barrier transparency

Cited by in corpus (5)

• Fabrication Process and Properties of Fully-Planarized Deep-Submicron Nb/Al-AlOx/Nb Josephson Junctions for VLSI Circuits
• Delocalised oxygen as the origin of two-level defects in Josephson junctions
• Intrinsically shunted Josephson junctions for electronics applications
• Constructing ab initio models of ultra-thin Al-AlOx-Al barriers
• Tunneling through Al/AlOx/Al junction: analytical models and first principles simulations