Doping dependence of a quasi-1D cuprate investigated by resonant inelastic X-ray scattering*

The experimental investigation of one-dimensional spin chains is an important angle to benchmark theoretical frameworks tackling the physics of strongly correlated electron systems, such as the Hubbard model. Yet, relevant experimental studies are scarce due to the lack of dope-able 1D materials. Recently, thin films of the quasi-1D cuprate Ba_2-xCuO_3+d (BCO) were synthesized and successfully hole doped using molecular beam epitaxy (MBE). Here we present resonant inelastic x-ray scattering (RIXS) results on these quasi-1D spin chains. We identify dominant electronic and magnetic contributions to the RIXS cross section and the dependence of these spectral signatures as a function of doping. From these measurements, we find robust signatures of dispersive two-spinon and orbital excitations for doping concentrations exceeding 20%. Furthermore, we perform a comparison with numerical results invoking an extended 1D Hubbard model. The potential implications of our findings for higher dimensional cuprate systems will also be discussed.