Constructing ab initio models of ultra-thin Al-AlOx-Al barriers

TL;DR

This paper develops a computational methodology combining molecular mechanics, empirical, and ab initio methods to model ultra-thin amorphous aluminium-oxide barriers in Josephson junctions, aiding understanding of their structure and noise sources.

Contribution

It introduces a novel multi-scale modeling approach for atomic-scale structures of ultra-thin oxide barriers in superconducting devices.

Findings

Stable atomic models of aluminium-oxide barriers were constructed.

Barrier properties depend on density and stoichiometry.

Models align with experimental parameters.

Abstract

The microscopic structure of ultra-thin oxide barriers often plays a major role in modern nano-electronic devices. In the case of superconducting electronic circuits, their operation depends on the electrical non-linearity provided by one or more such oxide layers in the form of ultra-thin tunnel barriers (also known as Josephson junctions). Currently available fabrication techniques manufacture an amorphous oxide barrier, which is attributed as a major noise source within the device. The nature of this noise is currently an open question and requires both experimental and theoretical investigation. Here, we present a methodology for constructing atomic scale computational models of Josephson junctions using a combination of molecular mechanics, empirical and ab initio methods. These junctions consist of ultra-thin amorphous aluminium-oxide layers sandwiched between crystalline aluminium. The stability and structure of these barriers as a function of density and stoichiometry are investigated, which we compare to experimentally observed parameters