Effect of the chemical pressure on bimagnons in antiferromagnetic insulators: CaCuO2 and BaCuO2 studied with Cu-L3 resonant inelastic X-ray scattering

Substitution of Ca with Ba in CaCuO2 increases the lattice parameter which in turn modifies all interactions between the constituent ions. Here we study the effect on the bimagnon propagating in the Cu-O planes as seen with Resonant Inelastic X-ray Scattering at the Cu-L-3 peak. The bimagnon energy is reduced by a factor of 0.67 +/- 0.06 while its spectral weight decreases at least by a factor of 0.5. This scaling is understood from the dependence on superexchange, which is linear in the former case and quadratic in the second. Moreover the scaling of the bimagnon energy can be understood from the distance dependence of the transfer integrals.