Charge excitations in high-T_c superconducting copper oxides studied by resonant inelastic x-ray scattering

摘要

Momentum-dependent charge excitations in high-T_c superconducting copper oxides are investigated by resonant inelastic x-ray scattering at the Cu K-edge. An excitation across the Mott gap excitation is observed in parent materials and it shows a characteristic dispersion relation in the CuO_2 plane. The Mott gap excitation persists in carrier doped superconductors. When holes are doped, the dispersion becomes smaller, while the intensity of the Mott gap excitation concentrates at the Brillouin zone center upon electron doping. At the same time, an intraband excitation of doped carriers emerges below the gap in both hole- and electron-dope cases. The observed momentum dependence is consistent with a theoretical calculation based on a Hubbard model.