Momentum-resolved charge excitations in high-TcTc cuprates studied by resonant inelastic X-ray scattering

We report a Cu K  -edge resonant inelastic X-ray scattering (RIXS) study of high-TcTc cuprates. Momentum-resolved charge excitations in the CuO2 plane are examined from parent Mott insulators to carrier-doped superconductors. The Mott gap excitation in undoped insulators is found to commonly show a larger dispersion along the [π,π][π,π] direction than the [π,0][π,0] direction. On the other hand, the resonance condition displays material dependence. The Mott gap persists in carrier-doped states. Upon hole doping, the dispersion of the Mott gap excitation becomes weaker associated with the reduction of antiferromagnetic correlation and an intraband excitation appears as a continuum intensity below the gap at the same time. In the case of electron doping, the Mott gap excitation is prominent at the zone center and a dispersive intraband excitation is observed at finite momentum transfer.