Pu Yu, Department of Physics, Tsinghua University
Room 111, Physical Building
Electric-field control of phase transformation with ion transfer is of great interests in materials science with enormous practical applications. Due to the strong electron-ion interaction, the ionic evolution would naturally have dramatic influence on material functionalities. In this talk, I will first present a reversible and nonvolatile electric-field control of oxygen and hydrogen ion evolutions within the model system of brownmillerite SrCoO2.5 by ionic liquid gating. Due to the selectively controllable ionic evolutions, we achieved a tri-state phase transformations among SrCoO2.5 and its counterpart of perovskite SrCoO3-δ and a hitherto-unexplored HSrCoO2.5 phase. Because of the extremely distinct magnetic, electrical and optical properties among these three phases, this result forms solid foundation for conceptually new tri-state magnetoelectric and electrochromic effects. Along this vein, we further demonstrate the manipulation of metal-insulator transition and enhanced superconductivity through electric-field induced protonation in WO3 and iron-based superconductors, respectively. Finally, using Co/SrCoO2.5 as model system, I will introduce a new strategy to achieve the room temperature electric-field control of magnetic state in the Co layer accompanied by the bipolar resistance switch. In this case, the electric field controlled oxygen evolution leads to oxygen ion accumulation (gating) at the interface, in the same manner as the conventional charge-gating device. As the consequence, the interfacial oxygen contents modulate the magnetic interaction within the Co surface layer and eventually results in the intriguing magnetoelectric coupling. We envision that the ionic evolution brings in a new tuning knob to manipulate the coupling and correlation between charge, spin, orbital and lattice degrees of freedom and paves a new playground for the discovery of novel materials and rich functionalities.