47 research outputs found

    Intra-layer doping effects on the high-energy magnetic correlations in NaFeAs

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    We have used Resonant Inelastic X-ray Scattering (RIXS) and dynamical susceptibility calculations to study the magnetic excitations in NaFe1x_{1-x}Cox_xAs (x = 0, 0.03, and 0.08). Despite a relatively low ordered magnetic moment, collective magnetic modes are observed in parent compounds (x = 0) and persist in optimally (x = 0.03) and overdoped (x = 0.08) samples. Their magnetic bandwidths are unaffected by doping within the range investigated. High energy magnetic excitations in iron pnictides are robust against doping, and present irrespectively of the ordered magnetic moment. Nevertheless, Co doping slightly reduces the overall magnetic spectral weight, differently from previous studies on hole-doped BaFe2_{2}As2_{2}, where it was observed constant. Finally, we demonstrate that the doping evolution of magnetic modes is different for the dopants being inside or outside the Fe-As layer.Comment: 19 pages, 7 figure

    Orbital breathing effects in the computation of x-ray d-ion spectra in solids by ab initio wave-function-based methods

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    In existing theoretical approaches to core-level excitations of transition-metal ions in solids relaxation and polarization effects due to the inner core hole are often ignored or described phenomenologically. Here we set up an ab initio computational scheme that explicitly accounts for such physics in the calculation of x-ray absorption and resonant inelastic x-ray scattering spectra. Good agreement is found with experimental transition-metal LL-edge data for the strongly correlated d9d^9 cuprate Li2_2CuO2_2, for which we determine the absolute scattering intensities. The newly developed methodology opens the way for the investigation of even more complex dnd^n electronic structures of group VI B to VIII B correlated oxide compounds

    Electron-lattice interactions strongly renormalize the charge transfer energy in the spin-chain cuprate Li2_2CuO2_2

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    Strongly correlated insulators are broadly divided into two classes: Mott-Hubbard insulators, where the insulating gap is driven by the Coulomb repulsion UU on the transition-metal cation, and charge-transfer insulators, where the gap is driven by the charge transfer energy Δ\Delta between the cation and the ligand anions. The relative magnitudes of UU and Δ\Delta 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 Li2_\mathrm{2}CuO2_\mathrm{2}, where Δ\Delta has a large non-electronic component. Combining resonant inelastic x-ray scattering with detailed modeling, 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\Delta, which significantly reshapes the fundamental electronic properties of Li2_\mathrm{2}CuO2_\mathrm{2}.Comment: Nature Communications, in pres

    Single- and Multimagnon Dynamics in Antiferromagnetic α\alpha-Fe2_2O3_3 Thin Films

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    Understanding the spin dynamics in antiferromagnetic (AFM) thin films is fundamental for designing novel devices based on AFM magnon transport. Here, we study the magnon dynamics in thin films of AFM S=5/2S=5/2 α\alpha-Fe2_2O3_3 by combining resonant inelastic x-ray scattering, Anderson impurity model plus dynamical mean-field theory, and Heisenberg spin model. Below 100 meV, we observe the thickness-independent (down to 15 nm) acoustic single-magnon mode. At higher energies (100-500 meV), an unexpected sequence of equally spaced, optical modes is resolved and ascribed to ΔSz=1\Delta S_z = 1, 2, 3, 4, and 5 magnetic excitations corresponding to multiple, noninteracting magnons. Our study unveils the energy, character, and momentum-dependence of single and multimagnons in α\alpha-Fe2_2O3_3 thin films, with impact on AFM magnon transport and its related phenomena. From a broader perspective, we generalize the use of L-edge resonant inelastic x-ray scattering as a multispin-excitation probe up to ΔSz=2S\Delta S_z = 2S. Our analysis identifies the spin-orbital mixing in the valence shell as the key element for accessing excitations beyond ΔSz=1\Delta S_z = 1, and up to, e.g., ΔSz=5\Delta S_z = 5. At the same time, we elucidate the novel origin of the spin excitations beyond the ΔSz=2\Delta S_z = 2, emphasizing the key role played by the crystal lattice as a reservoir of angular momentum that complements the quanta carried by the absorbed and emitted photons.Comment: Accepted in Physical Review

    Determining the Short-Range Spin Correlations in Cuprate Chain Materials with Resonant Inelastic X-ray Scattering

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    We report a high-resolution resonant inelastic soft x-ray scattering study of the quantum magnetic spin-chain materials Li2CuO2 and CuGeO3. By tuning the incoming photon energy to the oxygen K-edge, a strong excitation around 3.5 eV energy loss is clearly resolved for both materials. Comparing the experimental data to many-body calculations, we identify this excitation as a Zhang-Rice singlet exciton on neighboring CuO4-plaquettes. We demonstrate that the strong temperature dependence of the inelastic scattering related to this high-energy exciton enables to probe short-range spin correlations on the 1 meV scale with outstanding sensitivity.Comment: 5 pages, 4 figure
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