title: Nonlinear lattice dynamics as a basis for enhanced superconductivity in YBa2Cu3O6.5.
abstract: Terahertz-frequency optical pulses can resonantly drive selected vibrational modes in solids and deform their crystal structures. In complex oxides, this method has been used to melt electronic order, drive insulator-to-metal transitions and induce superconductivity. Strikingly, coherent interlayer transport strongly reminiscent of superconductivity can be transiently induced up to room temperature (300 kelvin) in YBa2Cu3O6+x (refs 9, 10). Here we report the crystal structure of this exotic non-equilibrium state, determined by femtosecond X-ray diffraction and ab initio density functional theory calculations. We find that nonlinear lattice excitation in normal-state YBa2Cu3O6+x at above the transition temperature of 52 kelvin causes a simultaneous increase and decrease in the Cu-O2 intra-bilayer and, respectively, inter-bilayer distances, accompanied by anisotropic changes in the in-plane O-Cu-O bond buckling. Density functional theory calculations indicate that these motions cause drastic changes in the electronic structure. Among these, the enhancement in the character of the in-plane electronic structure is likely to favour superconductivity.
authors.affiliation: 1] Max Planck Institute for the Structure and Dynamics of Matter, 22761 Hamburg, Germany [2] University of Hamburg, 22761 Hamburg, Germany [3] Center for Free-Electron Laser Science (CFEL), 22761 Hamburg, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Mankowsky
authors.affiliation: Centre de Physique Théorique, École Polytechnique, CNRS, 91128 Palaiseau Cedex, France.
authors.forename: A
authors.initials: A
authors.lastname: Subedi
authors.affiliation: 1] Max Planck Institute for the Structure and Dynamics of Matter, 22761 Hamburg, Germany [2] Center for Free-Electron Laser Science (CFEL), 22761 Hamburg, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Först
authors.affiliation: Swiss Light Source, Paul Scherrer Institut, 5232 Villigen, Switzerland.
authors.forename: S O
authors.initials: SO
authors.lastname: Mariager
authors.affiliation: Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park 94025, California, USA.
authors.forename: M
authors.initials: M
authors.lastname: Chollet
authors.affiliation: Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park 94025, California, USA.
authors.forename: H T
authors.initials: HT
authors.lastname: Lemke
authors.affiliation: Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park 94025, California, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: Robinson
authors.affiliation: Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park 94025, California, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Glownia
authors.affiliation: Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park 94025, California, USA.
authors.forename: M P
authors.initials: MP
authors.lastname: Minitti
authors.affiliation: Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Frano
authors.affiliation: Materials Theory, Eidgenössische Technische Hochschule Zürich, 8093 Zürich, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Fechner
authors.affiliation: Materials Theory, Eidgenössische Technische Hochschule Zürich, 8093 Zürich, Switzerland.
authors.forename: N A
authors.initials: NA
authors.lastname: Spaldin
authors.affiliation: Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Loew
authors.affiliation: Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Keimer
authors.affiliation: 1] Centre de Physique Théorique, École Polytechnique, CNRS, 91128 Palaiseau Cedex, France [2] Collège de France, 11 place Marcelin Berthelot, 75005 Paris, France [3] Département de Physique de la Matière Condensée (MaNEP), Université de Genève, 1211 Genève, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Georges
authors.affiliation: 1] Max Planck Institute for the Structure and Dynamics of Matter, 22761 Hamburg, Germany [2] University of Hamburg, 22761 Hamburg, Germany [3] Center for Free-Electron Laser Science (CFEL), 22761 Hamburg, Germany [4] Department of Physics, University of Oxford, Clarendon Laboratory, Oxford OX1 3PU, UK.
authors.forename: A
authors.initials: A
authors.lastname: Cavalleri