Ionic Control of Emergent Physical Phenomena in Epitaxial Oxide Thin Films

Iontronics is an emerging science and technology that shows fascinating physical phenomena, particularly in oxide thin films controlled by ionic motion and arrangement. The most significant impact of iontronics is that iontronic devices enable us to control exotic physical properties, such as insulator-metal transitions, emergent superconductivity, and tunable magnetism, which are extremely difficult or even impossible with conventional field-effect-transistors. Here, we show how the oxygen vacancy channels (OVCs) in brownmillerite SrCoO_2.5 thin films can be manipulated via ionic gating (IG). In addition, we demonstrate the epitaxial growth of single-domain <i>T</i>-Nb₂O₅ thin films, for the first time, critically with the ion channels oriented perpendicular to the film’s surface. We show that the insertion of just a small amount of Li via IG results in a colossal insulator to metal transition with almost eleven orders of magnitude decrease in resistivity. In situ experiments, in conjunction with theoretical calculations, reveal a series of transitions between distinct crystal and electronic structures as the Li content is systematically increased. These include hidden phases that have not previously been identified. Furthermore, by replacing the conventional Au gate electrode with Li-containing gate electrodes, tunable and low voltage operation via Li-chemical potential control is demonstrated. Finally, we present a new concept to tailor octahedral distortion, magnetism, and anomalous Hall effect in ferromagnetic SrRuO₃ thin films via hydrogenation. These findings open a new path towards the exploration of hidden phases and the development of novel electrochemically controlled electronic devices.