title: Electron-lattice interactions strongly renormalize the charge-transfer energy in the spin-chain cuprate Li2CuO2.
abstract: Strongly correlated insulators are broadly divided into two classes: Mott-Hubbard insulators, where the insulating gap is driven by the Coulomb repulsion U on the transition-metal cation, and charge-transfer insulators, where the gap is driven by the charge-transfer energy Δ between the cation and the ligand anions. The relative magnitudes of U and Δ determine which class a material belongs to, and subsequently the nature of its low-energy excitations. These energy scales are typically understood through the local chemistry of the active ions. Here we show that the situation is more complex in the low-dimensional charge-transfer insulator Li2CuO2, where Δ has a large non-electronic component. Combining resonant inelastic X-ray scattering with detailed modelling, we determine how the elementary lattice, charge, spin and orbital excitations are entangled in this material. This results in a large lattice-driven renormalization of Δ, which significantly reshapes the fundamental electronic properties of Li2CuO2.
authors.affiliation: Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996, USA.
authors.forename: Steve
authors.identifier: http://orcid.org/0000-0002-2343-0113
authors.initials: S
authors.lastname: Johnston
authors.affiliation: Research Department Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut, CH-5232, Villigen, Switzerland.|Department of Physics, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
authors.forename: Claude
authors.initials: C
authors.lastname: Monney
authors.affiliation: Leibniz Institute for Solid State and Materials Research, IFW Dresden, Helmholtzstrasse 20, D-01171 Dresden, Germany.|National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, New York 11973-5000, USA.
authors.forename: Valentina
authors.initials: V
authors.lastname: Bisogni
authors.affiliation: Research Department Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut, CH-5232, Villigen, Switzerland.|Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, UK.
authors.forename: Ke-Jin
authors.initials: KJ
authors.lastname: Zhou
authors.affiliation: Leibniz Institute for Solid State and Materials Research, IFW Dresden, Helmholtzstrasse 20, D-01171 Dresden, Germany.
authors.forename: Roberto
authors.initials: R
authors.lastname: Kraus
authors.affiliation: Leibniz Institute for Solid State and Materials Research, IFW Dresden, Helmholtzstrasse 20, D-01171 Dresden, Germany.
authors.forename: Günter
authors.initials: G
authors.lastname: Behr
authors.affiliation: Research Department Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut, CH-5232, Villigen, Switzerland.
authors.forename: Vladimir N
authors.initials: VN
authors.lastname: Strocov
authors.affiliation: Institute of Physics, ASCR, Na Slovance 2, CZ-18221 Praha 8, Czech Republic.
authors.forename: Jiři
authors.initials: J
authors.lastname: Málek
authors.affiliation: Leibniz Institute for Solid State and Materials Research, IFW Dresden, Helmholtzstrasse 20, D-01171 Dresden, Germany.
authors.forename: Stefan-Ludwig
authors.initials: SL
authors.lastname: Drechsler
authors.affiliation: Leibniz Institute for Solid State and Materials Research, IFW Dresden, Helmholtzstrasse 20, D-01171 Dresden, Germany.
authors.forename: Jochen
authors.initials: J
authors.lastname: Geck
authors.affiliation: Research Department Synchrotron Radiation and Nanotechnology, Paul Scherrer Institut, CH-5232, Villigen, Switzerland.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Schmitt
authors.affiliation: Leibniz Institute for Solid State and Materials Research, IFW Dresden, Helmholtzstrasse 20, D-01171 Dresden, Germany.|Department of Physics, TU Dresden, D-01062 Dresden, Germany.
authors.forename: Jeroen
authors.initials: J
authors.lastname: van den Brink