Electronic and magnetic excitations in the half-stuffed Cu-O planes of Ba2Cu3O4Cl2 measured by resonant inelastic x-ray scattering

Abstract

We use resonant inelastic x-ray scattering (RIXS) at the Cu ${\mathrm{L}}_{3}$ edge to measure the charge and spin excitations in the ``half-stuffed'' Cu-O planes of the cuprate antiferromagnet ${\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{4}{\mathrm{Cl}}_{2}$. The RIXS line shape reveals distinct contributions to the $dd$ excitations from the two structurally inequivalent Cu sites, which have different out-of-plane coordinations. The low-energy response exhibits magnetic excitations. We find a spin-wave branch whose dispersion follows the symmetry of a ${\mathrm{CuO}}_{2}$ sublattice, similar to the case of the ``fully stuffed'' planes of tetragonal CuO (T-CuO). Its bandwidth is closer to that of a typical cuprate material, such as ${\mathrm{Sr}}_{2}{\mathrm{CuO}}_{2}{\mathrm{Cl}}_{2}$, than it is to that of T-CuO. We interpret this result as arising from the absence of the effective four-spin inter-sublattice interactions that act to reduce the bandwidth in T-CuO.