Resonant inelastic X-ray scattering study of charge excitations in La2CuO4
Kim YJ, Hill JP, Burns CA, Wakimoto S, Birgeneau RJ, Casa D, Gog T, Venkataraman CT
PHYSICAL REVIEW LETTERS
89 (17): Art. No. 177003 OCT 21 2002
We report a resonant inelastic x-ray scattering study of the dispersion relations of charge-transfer excitations in insulating La2CuO4. These data reveal two peaks, both of which show two-dimensional characteristics. The lowest energy excitation has a gap energy of similar to2.2 eV at the zone enter, and a dispersion of similar to1 eV. The spectral weight of this mode becomes dramatically smaller around (pi, pi). The second peak shows a smaller dispersion (similar to0.5 eV) with a zone-center energy of similar to3.9 eV. We argue that these are both highly dispersive exciton modes damped by the presence of the electron-hole continuum.