title: In operando evidence of deoxygenation in ionic liquid gating of YBa2Cu3O7-X.
abstract: 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 VO2by 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 YBa2Cu3O7-X(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.
authors.affiliation: 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.
authors.forename: Ana M
authors.initials: AM
authors.lastname: Perez-Muñoz
authors.affiliation: Physics of Complex Materials Group (GFMC), Dpto. Física de Materiales, Universidad Complutense de Madrid, 28040 Madrid, Spain.|Plane Grating Monochromator Beamline, Brazilian Synchrotron Light Source, National Center for Research in Energy and Materials, Campinas, 13083-100 Sao Paulo, Brazil.
authors.forename: Pedro
authors.initials: P
authors.lastname: Schio
authors.affiliation: Science et Ingénierie des Matériaux et Procédes, CNRS, Université Grenoble Alpes, F-38000 Grenoble, France.
authors.forename: Roberta
authors.initials: R
authors.lastname: Poloni
authors.affiliation: Institut des Sciences de la Terre, CNRS, Université Grenoble Alpes, F-38000 Grenoble, France.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Fernandez-Martinez
authors.affiliation: Physics of Complex Materials Group (GFMC), Dpto. Física de Materiales, Universidad Complutense de Madrid, 28040 Madrid, Spain.
authors.forename: Alberto
authors.initials: A
authors.lastname: Rivera-Calzada
authors.affiliation: Plane Grating Monochromator Beamline, Brazilian Synchrotron Light Source, National Center for Research in Energy and Materials, Campinas, 13083-100 Sao Paulo, Brazil.
authors.forename: Julio C
authors.identifier: 0000-0002-7904-6874
authors.initials: JC
authors.lastname: Cezar
authors.affiliation: Spanish Collaborating Research Group, Beamline BM25, European Radiation Synchrotron Facility, F-38043 Grenoble Cedex 9, France.|Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas, 28049 Madrid, Spain.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Salas-Colera
authors.affiliation: Spanish Collaborating Research Group, Beamline BM25, European Radiation Synchrotron Facility, F-38043 Grenoble Cedex 9, France.|Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas, 28049 Madrid, Spain.
authors.forename: German R
authors.identifier: 0000-0003-4251-3245
authors.initials: GR
authors.lastname: Castro
authors.affiliation: School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455.
authors.forename: Joseph
authors.initials: J
authors.lastname: Kinney
authors.affiliation: Physics of Complex Materials Group (GFMC), Dpto. Física de Materiales, Universidad Complutense de Madrid, 28040 Madrid, Spain.|GFMC, Instituto de Magnetismo Aplicado, 28040 Madrid, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Leon
authors.affiliation: Physics of Complex Materials Group (GFMC), Dpto. Física de Materiales, Universidad Complutense de Madrid, 28040 Madrid, Spain.|GFMC, Instituto de Magnetismo Aplicado, 28040 Madrid, Spain.
authors.forename: Jacobo
authors.initials: J
authors.lastname: Santamaria
authors.affiliation: Physics of Complex Materials Group (GFMC), Dpto. Física de Materiales, Universidad Complutense de Madrid, 28040 Madrid, Spain; javigb@umn.edu.|Characterization Facility, University of Minnesota, Minneapolis, MN 55455.
authors.forename: Javier
authors.initials: J
authors.lastname: Garcia-Barriocanal
authors.affiliation: School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455.
authors.forename: Allen M
authors.initials: AM
authors.lastname: Goldman
keywords: electric double-layer techniques; first-principles density functional theory; high-temperature superconductivity; near-edge X-ray absorption spectroscopies; superconductor-insulator transition