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arXiv · 1102.0139

Universality of transport properties of ultra-thin oxide films

V. Lacquaniti·M. Belogolovskii·C. Cassiago·N. De Leo·M. Fretto·A. Sosso
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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.

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V. Lacquaniti, M. Belogolovskii, C. Cassiago, N. De Leo, M. Fretto, A. Sosso. 2012-04-10. Universality of transport properties of ultra-thin oxide films. https://doi.org/10.1088/1367-2630%2F14%2F2%2F023025

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