title: Atomic structure and oxygen deficiency of the ultrathin aluminium oxide barrier in Al/AlOx/Al Josephson junctions.
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.
authors.affiliation: Department of Applied Physics, Chalmers University of Technology, 41296, Göteborg, Sweden.
authors.forename: Lunjie
authors.initials: L
authors.lastname: Zeng
authors.affiliation: Department of Materials and Environmental Chemistry, Stockholm University, 10691, Stockholm, Sweden.
authors.forename: Dung Trung
authors.initials: DT
authors.lastname: Tran
authors.affiliation: Department of Materials and Environmental Chemistry, Stockholm University, 10691, Stockholm, Sweden.
authors.forename: Cheuk-Wai
authors.initials: CW
authors.lastname: Tai
authors.affiliation: Department of Materials and Environmental Chemistry, Stockholm University, 10691, Stockholm, Sweden.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Svensson
authors.affiliation: Department of Applied Physics, Chalmers University of Technology, 41296, Göteborg, Sweden.
authors.forename: Eva
authors.initials: E
authors.lastname: Olsson