Resonant inelastic x-ray scattering study of intraband charge excitations in hole-doped high-T_c cuprates

We have performed resonant inelastic x-ray scattering (RIXS) near the Cu-K edge on cuprate superconductors La_2-xSr_xCuO₄, La_2-xBa_xCuO₄, La_2-xSr _xCu_1-yFe_yO₄, and Bi _1.76Pb_0.35Sr_1.89CuO_6+δ, covering underdoped to heavily overdoped regimes and focusing on charge excitations inside the charge-transfer gap. RIXS measurements of the 214 systems with E_i=8.993 keV have revealed that the RIXS intensity at 1-eV energy transfer has a minimum at (0,0) and maxima at (±0.4π,0) and (0,±0.4π) for all doping points regardless of the stripe-ordered state, suggesting that the corresponding structure is not directly related to stripe order. Measurements with E_i=9.003 keV on metallic La _1.7Sr_0.3CuO₄ and Bi_1.76Pb _0.35Sr_1.89CuO_6+δ exhibit a dispersive intraband excitation below 4 eV, similar to that observed in the electron-doped Nd_1.85Ce_0.15CuO₄. This is the first observation of a dispersive intraband excitation in a hole-doped system, evidencing that both electron- and hole-doped systems have a similar dynamical charge correlation function.