Electronic structure of doped lanthanum cuprates studied with resonant inelastic x-ray scattering

摘要

We report a comprehensive Cu K-edge resonant inelastic x-ray scattering (RIXS) investigation of La_(2_x)Sr_xCuO_4 (LSCO) for 0≤ x ≤0.35, stripe-ordered La_(1.875)Bao_(0.125)CuO_4 (LBCO), and La_2Cu_(0.96)Ni_(0.04)O_4 (LCNO) crystals. The RIXS spectra measured at three high-symmetry momentum-transfer (q) positions are compared as a function of doping and for the different dopants. The spectra in the energy range 1-6 eV can be described with three broad peaks, which evolve systematically with increased doping. The most systematic trend was observed for q = (π,0) corresponding to the zone boundary. As hole doping increased, the spectral weight transfer from high energies to low energies is nearly linear with x at this q. We interpret the peaks as interband transitions in the context of existing band models for this system, assigning them to Zhang-Rice band→upper Hubbard band, lower-lying band→upper Hubbard band, and lower-lying band→Zhang-Rice band transitions. The spectrum of stripe-ordered LBCO was also measured, and found to be identical to the correspondingly doped LSCO, except for a relative enhancement of the near-infrared peak intensity at ~1.5-1.7 eV. The temperature dependence of this near-infrared peak in LBCO was more pronounced than for other parts of the spectrum, continuously decreasing in intensity as the temperature was raised from 25 to 300 K. Finally, we find that 4% Ni substitution in the Cu site has a similar effect on the spectra as does Sr substitution in the La site.