Resonant Inelastic X-Ray Scattering Study of Charge Excitations inLa2CuO4

Abstract

We report a resonant inelastic x-ray scattering study of the dispersion relations of charge-transfer excitations in insulating $\mathrm{L}{\mathrm{a}}_{\mathrm{2}}\mathrm{C}\mathrm{u}{\mathrm{O}}_{\mathrm{4}}$. These data reveal two peaks, both of which show two-dimensional characteristics. The lowest energy excitation has a gap energy of $\sim 2.2\mathrm{e}\mathrm{V}$ at the zone enter, and a dispersion of $\sim 1\mathrm{e}\mathrm{V}$. The spectral weight of this mode becomes dramatically smaller around ($\pi$, $\pi$). The second peak shows a smaller dispersion ($\sim 0.5\mathrm{e}\mathrm{V}$) with a zone-center energy of $\sim 3.9\mathrm{e}\mathrm{V}$. We argue that these are both highly dispersive exciton modes damped by the presence of the electron-hole continuum.