Solid-State Electrochemical Switch of Superconductor-Metal-Insulators

Controlling the oxygen content can manipulate the electrical conductivity of transition metal oxides (TMOs). Although the superconductor-metal-insulator transition is useful for functional devices, an electrical path must be developed to manipulate the oxygen deficiency (δ) while maintaining the solid state. YBa₂Cu₃O_7-δ (YBCO, 0 ≤ δ ≤ 1) is a high transition temperature (T_c) TMO that can be modulated from a superconductor (T_c ≈ 92 K when δ = 0) to an insulator (δ ≈ 1). Here, we show a simple and efficient way to manipulate δ in YBCO films using a solid-state electrochemical redox treatment. Applying a negative voltage injects oxide ions to the YBCO films, increasing T_c. Employing a positive voltage suppresses the superconducting transition and modulates the electrical conductivity. The present results demonstrate that the superconductor-metal-insulator transition of YBCO is modulated electrochemically in the solid state, opening possibilities of superconducting oxide-based device applications.