Fast Track to the Overdoped Regime of Superconducting YBa ₂ Cu ₃ O _7‐δ Thin Films via Electrochemical Oxidation

ABSTRACT High temperature superconductors, especially YBa 2 Cu 3 O 7‐δ (YBCO), are considered a key enabling technology toward a clean energy future. Hole doping in YBCO is a prerequisite for the emergence of its unchallenged superconducting properties. Up to now, research was focused on the under‐ and optimally doped region, due to practical limitations in reaching the overdoped state, despite being highly interesting from fundamental and applied aspects as competing orders vanish and critical current densities are expected to peak. Here, we deploy for the first time an electrochemical method to access the mostly uncharted overdoped region. We demonstrate precise control over the bulk oxygen concentration in YBCO thin films across the full off‐stoichiometry window () using electrochemical oxidation combined with in situ X‐ray diffraction (XRD) and electrical measurements. Resulting high doping states and critical current densities are confirmed using a multi modal approach, including XRD, electrical, Hall and magnetic characterization. Thus, this work opens a promising pathway based on electrochemical oxidation toward electronically clean, oxygen overdoped cuprate superconductors and therefore will assist to further push the critical current density to its intrinsic limit.