Perez-Muñoz Ana M, Schio Pedro, Poloni Roberta, Fernandez-Martinez Alejandro, Rivera-Calzada Alberto, Cezar Julio C, Salas-Colera Eduardo, Castro German R, Kinney Joseph, Leon Carlos, Santamaria Jacobo, Garcia-Barriocanal Javier, Goldman Allen M
Physics of Complex Materials Group (GFMC), Dpto. Física de Materiales, Universidad Complutense de Madrid, 28040 Madrid, Spain.
Campus of International Excellence Campus Moncloa, Universidades Complutense y Politécnica de Madrid, 28040 Madrid, Spain.
Proc Natl Acad Sci U S A. 2017 Jan 10;114(2):215-220. doi: 10.1073/pnas.1613006114. Epub 2016 Dec 27.
Field-effect experiments on cuprates using ionic liquids have enabled the exploration of their rich phase diagrams [Leng X, et al. (2011) Phys Rev Lett 107(2):027001]. Conventional understanding of the electrostatic doping is in terms of modifications of the charge density to screen the electric field generated at the double layer. However, it has been recently reported that the suppression of the metal to insulator transition induced in VO by ionic liquid gating is due to oxygen vacancy formation rather than to electrostatic doping [Jeong J, et al. (2013) Science 339(6126):1402-1405]. These results underscore the debate on the true nature, electrostatic vs. electrochemical, of the doping of cuprates with ionic liquids. Here, we address the doping mechanism of the high-temperature superconductor YBaCuO (YBCO) by simultaneous ionic liquid gating and X-ray absorption experiments. Pronounced spectral changes are observed at the Cu K-edge concomitant with the superconductor-to-insulator transition, evidencing modification of the Cu coordination resulting from the deoxygenation of the CuO chains, as confirmed by first-principles density functional theory (DFT) simulations. Beyond providing evidence of the importance of chemical doping in electric double-layer (EDL) gating experiments with superconducting cuprates, our work shows that interfacing correlated oxides with ionic liquids enables a delicate control of oxygen content, paving the way to novel electrochemical concepts in future oxide electronics.
利用离子液体对铜酸盐进行的场效应实验，使得人们能够探索其丰富的相图[冷X等人（2011年），《物理评论快报》107(2):027001]。对静电掺杂的传统理解是，通过改变电荷密度来屏蔽双层处产生的电场。然而，最近有报道称，离子液体门控在VO中诱导的金属到绝缘体转变的抑制，是由于氧空位的形成而非静电掺杂[郑J等人（2013年），《科学》339(6126):1402 - 1405]。这些结果突显了关于用离子液体对铜酸盐进行掺杂的真正本质（静电与电化学）的争论。在此，我们通过同时进行离子液体门控和X射线吸收实验来研究高温超导体YBaCuO（YBCO）的掺杂机制。在Cu K边观察到明显的光谱变化，同时伴随着超导体到绝缘体的转变，这证明了CuO链脱氧导致的Cu配位的改变，第一性原理密度泛函理论（DFT）模拟证实了这一点。除了为化学掺杂在超导铜酸盐的电双层（EDL）门控实验中的重要性提供证据外，我们的工作还表明，将相关氧化物与离子液体相结合能够精确控制氧含量，为未来氧化物电子学中的新型电化学概念铺平了道路。
