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- Kuiper, Pieter, 1960-, et al.
(författare)
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Polarization-dependent nickel 2p x-ray-absorption spectra of La2NiO4+δ
- 1998
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Ingår i: Physical Review B Condensed Matter. - College Park, MD : American Physical Society. - 0163-1829 .- 1095-3795. ; 57:3, s. 1552-1557
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Tidskriftsartikel (refereegranskat)abstract
- We present polarization dependent x-ray-absorption spectra at nickel L edges of well-characterized La2NiO4+δ single crystals. In the stoichiometric compound the splitting between the x2−y2 and the 3z2−r2 orbitals is 0.7 eV, according to a fit of the 2p53d9 multiplet to the spectra. This value is in agreement with an assignment of dd excitations of the optical spectrum. The Ni L edges of the doped compound are consistent with the isotropic prepeak observed at the oxygen 1s edge. Theory does not predict holes on the apex oxygens, but we argue that doping causes a polaronic deformation which reduces the tetragonal distortion of the NiO6 octahedra, and delocalizes the hole over all six ligands.
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| 2. |
- Kuiper, Pieter, 1960-, et al.
(författare)
-
Resonant X-Ray raman spectra of Cu dd excitations in Sr2CuO2Cl2
- 1998
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Ingår i: Physical Review Letters. - College Park, MD : American Physical Society. - 0031-9007 .- 1079-7114. ; 80:23, s. 5204-5207
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Tidskriftsartikel (refereegranskat)abstract
- We present resonant x-ray Raman scattering results on Sr2CuO2Cl2, a model compound for high- Tc superconductors. We demonstrate that the dd excitations can be observed and show that the polarization dependence can be used to identify the dd excitations. We find the transition from the dx2−y2 ground state to the dxy excited state at 1.35 eV and to the degenerate dxz and dyz excited states at 1.7 eV. From analysis of the polarization dependence we conclude that the d3z2−r2 orbital energy is at 1.5 eV and not in the midinfrared (0.5 eV) as recently suggested. We use recent theoretical arguments to show that the d3z2−r2 excitation is accompanied by a local spin flip resulting in a shift upwards of 0.2 eV due to the exchange interaction with the neighboring spins. ©1998 American Physical Society.
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