Manipulation of electrical performance in Al-based Josephson junctions via oxygen vacancies in barrier†

Abstract

Defects in the Al-based Josephson junctions, particularly oxygen vacancy (OV) defects in the barrier, are key determinants for the performance of superconducting qubits, directly limiting the coherence time. However, the effects of OVs with different positions and distributions in the barrier on the performance of Josephson junctions (JJs) remain unclear. Here, we reveal that the electronic structures and transport properties of Al/AlO_X/Al JJs are highly dependent on the positions of OVs in the barrier by developing JJ models incorporating different positions, distributions, and numbers of OVs. The OVs in the barrier contribute to improving the conductance of the device. This can be attributed to the fact that the Coulomb repulsion among Al ions in proximity to OVs induces electron delocalization, thereby altering the local density of states in the barrier. Specifically, different positions of OVs can cause variations in electrical properties by several orders of magnitude, when maintaining a fixed number and distribution of OVs. Moreover, the distribution and number of vacancies also affect the electrical properties of JJ to some extent. These results provide theoretical guidance for the study of the microscopic mechanism of JJ with defects, indicating a promising potential for manipulating the performance of JJs.