Momentum dependence of charge excitations in YBaCuO and NdCeCuO

Ishii, Kenji

We have carried out resonant inelastic X-ray scattering (RIXS) studies on two high-Tc superconductors at the optimal carrier concentration, YBaCuO (YBCO) and NdCeCuO (NCCO). Using a twin-free YBCO, we could successfully differentiate the Mott gap excitation in the CuO chain from that in the CuO plane, that is, the excitation in the chain is enhanced at 2 eV near the zone boundary of the chain direction, while the excitation in the plane is broad and almost independent of the momentum transfer. Furthremore we found that the Mott gap of the chain is smaller than that of the plane. In NCCO, we observed intraband excitation in the upper Hubbard band for the first time by tuning the incident energy of X-ray to the condition that the intraband is enhanced. The observed momentum dependence of the intraband excitation is similar to that of the dynamical density response function of the two-dimensional Hubbard model.