Observation of momentum-dependent charge excitations in hole-doped cuprates using resonant inelastic x-ray scattering at the oxygen K edge

We investigate electronic excitations in La_2-x(Br,Sr)ₓCuO₄ using resonant inelastic x-ray scattering (RIXS) at the oxygen K edge. RIXS spectra of the hole-doped cuprates show clear momentum dependence below 1 eV. The broad spectral weight exhibits positive dispersion and shifts to higher energy with increasing hole concentration. Theoretical calculation of the dynamical charge structure factor on oxygen orbitals in a three-band Hubbard model is consistent with the experimental observation of the momentum and doping dependence, and therefore the momentum-dependent spectral weight is ascribed to intraband charge excitations which have been observed in electron-doped cuprates. Our results confirm that the momentum-dependent charge excitations exist on the order of the transfer energy (t), and the broad spectral line shape indicates damped and incoherent character of the charge excitations at the energy range in the doped Mott insulators.