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. YBa2Cu3O7−δ (YBCO, 0 ≤ δ ≤ 1) is a high transition temperature (Tc) TMO that can be modulated from a superconductor (Tc ≈ 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 Tc. 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.