Disorder-free electrochemical doping of charge carriers into epitaxial La₂CuO_4+y films

Interesting new electronic phases in oxides can be explored by tuning parameters like external fields, chemical composition, epitaxial strain, etc. However, doping oxide heterostructures by chemical substitution or by variation of the oxygen stoichiometry usually comes at the expense of significant disorder which can negatively affect the desired ground state.
In this talk, I will outline a new, controlled approach to alter the oxygen concentration in thin films of La₂CuO_4+y using ex-situ electrochemistry. By allowing the oxygen ions to also penetrate into the substrate, we produce a lattice distortion in it. This modified structure is later stabilized in the film as well, due to the epitaxial relationship with the substrate. This results in high superconducting transition temperatures and novel structural dopant order with long-range coherence - reminiscent of 245 iron-selenide superconductors. Thus, I will demonstrate a general method to introduce interlayer oxygen with low disorder and applicability throughout a wide range of oxide heterostructures.