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Atomic structure and oxygen deficiency of the ultrathin aluminium oxide barrier in Al/AlOx/Al Josephson junctions.

Zeng L, Tran DT, Tai CW, Svensson G, Olsson E - Sci Rep (2016)

Bottom Line: The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier.In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide.Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Physics, Chalmers University of Technology, 41296, Göteborg, Sweden.

ABSTRACT
Al/AlOx/Al Josephson junctions are the building blocks of a wide range of superconducting quantum devices that are key elements for quantum computers, extremely sensitive magnetometers and radiation detectors. The properties of the junctions and the superconducting quantum devices are determined by the atomic structure of the tunnel barrier. The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier. Here we show that the miniaturized dimension of the barrier and the interfacial interaction between crystalline Al and amorphous AlOx give rise to oxygen deficiency at the metal/oxide interfaces. In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide. Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits.

No MeSH data available.


Related in: MedlinePlus

Structure models of Al-AlOx-Al junction and the corresponding PDFs.(a) Initial structure model built by Monte Carlo (MC) simulation. (b) Initial MC model’s PDF compared with the experimental NBED-PDF. (c) RMC-refined model. (d) RMC-refined model’s PDF fitted to the experimental NBED-PDF.
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f3: Structure models of Al-AlOx-Al junction and the corresponding PDFs.(a) Initial structure model built by Monte Carlo (MC) simulation. (b) Initial MC model’s PDF compared with the experimental NBED-PDF. (c) RMC-refined model. (d) RMC-refined model’s PDF fitted to the experimental NBED-PDF.

Mentions: In order to extract more detailed structural information, a model was built and compared with the experimental NBED-PDF. The model structure of AlOx was obtained from MC calculation (see Methods) and sandwiched between fcc Al layers to form an initial model of an Al-AlOx-Al junction (Fig. 3a). All the featured peaks (P1-P6) in the experimental NBED-PDF can be identified by the model PDF to a first approximation, confirming the above qualitative interpretation of the NBED-PDF (Fig. 3b). According to the atomic resolution STEM images (e.g. Fig. 1b), the Al lattice plane at the Al/AlOx interface is usually highly distorted, indicating strong Al-AlOx interaction at the metal/oxide interfaces. RMC refinement was then carried out by making the model PDF compatible with the experimental NBED-PDF22, through adaption of the structure of AlOx and introduction of local dislocations to the metallic Al layers close to the interfaces (see Methods, Fig. 3c,d).


Atomic structure and oxygen deficiency of the ultrathin aluminium oxide barrier in Al/AlOx/Al Josephson junctions.

Zeng L, Tran DT, Tai CW, Svensson G, Olsson E - Sci Rep (2016)

Structure models of Al-AlOx-Al junction and the corresponding PDFs.(a) Initial structure model built by Monte Carlo (MC) simulation. (b) Initial MC model’s PDF compared with the experimental NBED-PDF. (c) RMC-refined model. (d) RMC-refined model’s PDF fitted to the experimental NBED-PDF.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4940733&req=5

f3: Structure models of Al-AlOx-Al junction and the corresponding PDFs.(a) Initial structure model built by Monte Carlo (MC) simulation. (b) Initial MC model’s PDF compared with the experimental NBED-PDF. (c) RMC-refined model. (d) RMC-refined model’s PDF fitted to the experimental NBED-PDF.
Mentions: In order to extract more detailed structural information, a model was built and compared with the experimental NBED-PDF. The model structure of AlOx was obtained from MC calculation (see Methods) and sandwiched between fcc Al layers to form an initial model of an Al-AlOx-Al junction (Fig. 3a). All the featured peaks (P1-P6) in the experimental NBED-PDF can be identified by the model PDF to a first approximation, confirming the above qualitative interpretation of the NBED-PDF (Fig. 3b). According to the atomic resolution STEM images (e.g. Fig. 1b), the Al lattice plane at the Al/AlOx interface is usually highly distorted, indicating strong Al-AlOx interaction at the metal/oxide interfaces. RMC refinement was then carried out by making the model PDF compatible with the experimental NBED-PDF22, through adaption of the structure of AlOx and introduction of local dislocations to the metallic Al layers close to the interfaces (see Methods, Fig. 3c,d).

Bottom Line: The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier.In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide.Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Physics, Chalmers University of Technology, 41296, Göteborg, Sweden.

ABSTRACT
Al/AlOx/Al Josephson junctions are the building blocks of a wide range of superconducting quantum devices that are key elements for quantum computers, extremely sensitive magnetometers and radiation detectors. The properties of the junctions and the superconducting quantum devices are determined by the atomic structure of the tunnel barrier. The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier. Here we show that the miniaturized dimension of the barrier and the interfacial interaction between crystalline Al and amorphous AlOx give rise to oxygen deficiency at the metal/oxide interfaces. In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide. Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits.

No MeSH data available.


Related in: MedlinePlus