Resonant inelastic x-ray scattering in electronically quasi-zero-dimensional CuB2O4

We present a resonant inelastic scattering (RIXS) study using of CuB2O4, which contains a lattice of CuO4 plaquettes electronically isolated by B+3 ions. The observed Cu K-edge spectra show a small number of well-separated features, and the simple electronic structure of CuB2O4 allows us to explore RIXS phenomenology. We find a low-energy feature that cannot be attributed to the same charge-transfer excitation discussed in other cuprates and is likely a d -> d transition thought to be forbidden under common considerations of K-edge RIXS.