Electron-lattice interactions strongly renormalize the charge-transfer energy in the spin-chain cuprate $Li_2CuO_2$

Johnston, Steve; Monney, Claude; Bisogni, Valentina; Zhou, Ke-Jin; Kraus, Roberto; Behr, Günter; Strocov, Vladimir N; Málek, Jiři; Drechsler, Stefan-Ludwig; Geck, Jochen; Schmitt, Thorsten; van den Brink, Jeroen (2016). Electron-lattice interactions strongly renormalize the charge-transfer energy in the spin-chain cuprate $Li_2CuO_2$. Nature Communications, 7:10563.

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 $Li_2CuO_2$, 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 $Li_2CuO_2$.

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 $Li_2CuO_2$, 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 $Li_2CuO_2$.

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