title: Oxygen Displacement in Cuprates under Ionic Liquid Field-Effect Gating.
abstract: We studied structural changes in a 5 unit cell thick La1.96Sr0.04CuO4 film, epitaxially grown on a LaSrAlO4 substrate with a single unit cell buffer layer, when ultra-high electric fields were induced in the film by applying a gate voltage between the film (ground) and an ionic liquid in contact with it. Measuring the diffraction intensity along the substrate-defined Bragg rods and analyzing the results using a phase retrieval method we obtained the three-dimensional electron density in the film, buffer layer, and topmost atomic layers of the substrate under different applied gate voltages. The main structural observations were: (i) there were no structural changes when the voltage was negative, holes were injected into the film making it more metallic and screening the electric field; (ii) when the voltage was positive, the film was depleted of holes becoming more insulating, the electric field extended throughout the film, the partial surface monolayer became disordered, and equatorial oxygen atoms were displaced towards the surface; (iii) the changes in surface disorder and the oxygen displacements were both reversed when a negative voltage was applied; and (iv) the c-axis lattice constant of the film did not change in spite of the displacement of equatorial oxygen atoms.
authors: MacDiarmid Institute for Advanced Materials &Nanotechnology, Robinson Research Institute, Victoria University of Wellington, Lower Hutt 5046, New Zealand.|Condensed Matter Physics &Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA.|Laboratory of Physics of Complex Matter (LPMC), École Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland.
authors: Guy
authors: G
authors: Dubuis
authors: Racah Institute of Physics, Hebrew University, Jerusalem, 91904, Israel.
authors: Yizhak
authors: Y
authors: Yacoby
authors: Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors: Hua
authors: H
authors: Zhou
authors: Applied Physics Department, Yale University, New Haven, Connecticut 06520, USA.
authors: Xi
authors: X
authors: He
authors: Condensed Matter Physics &Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors: Anthony T
authors: AT
authors: Bollinger
authors: Laboratory of Physics of Complex Matter (LPMC), École Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland.
authors: Davor
authors: D
authors: Pavuna
authors: National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors: Ron
authors: R
authors: Pindak
authors: Condensed Matter Physics &Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA.|Applied Physics Department, Yale University, New Haven, Connecticut 06520, USA.
authors: Ivan
authors: I
authors: Božović