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arXiv 1102.0139cond-mat.mes-hallcond-mat.supr-con
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超薄氧化物薄膜输运性质的普遍性

Universality of transport properties of ultra-thin oxide films

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

摘要:

我们报告的低温测量的电流-电压特性的高导电性Nb/Al-AlOx-Nb结的Al夹层的厚度范围从40到150 nm和超薄的障碍,通过扩散氧化的Al表面形成的。在超导状态下,这些器件显示出很强的亚隙电流泄漏。通过分析器件中的库珀对和准粒子电流,我们得出结论,与传统的隧道结相比,亚能隙电阻的强烈抑制源于Schep和Bauer早先提出的Al氧化物势垒中的双态分布。我们提出了一个简单的物理解释,它的来源在纳米厚的氧化膜有关它的强局部势垒高度波动所产生的氧空位在薄的氧化铝隧道势垒热氧化形成。

英文摘要:

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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