The Josephson junction is a crucial element in superconducting devices, and niobium is a
promising candidate for the superconducting material due to its large energy gap relative to
aluminum. AlO x has long been regarded as the highest quality oxide tunnel barrier and is
often used in niobium-based junctions. Here, we propose ZrO x as an alternative tunnel
barrier material for Nb electrodes. We theoretically estimate that zirconium oxide has
excellent oxygen retention properties and experimentally verify that there is no significant …