Correlation of the superconducting critical temperature with spin and orbital excitations in (CaxLa1-x)(Ba1.75-xLa0.25+x)Cu3Oy as measured by resonant inelastic x-ray scattering

Electronic spin and orbital (dd) excitation spectra of (CaxLa1-x)(Ba1.75-xLa0.25+x)Cu3Oy samples aremeasured by resonant inelastic x-ray scattering (RIXS). In this compound, T-c of samples with identical hole dopings is strongly affected by the Ca/Ba substitution x due to subtle variations in the lattice constants, while crystal symmetry and disorder as measured by linewidths are x independent. We examine two extreme values of x and two extreme values of hole-doping content y corresponding to antiferromagnetic and superconducting states. The x dependence of the spin-mode energies is approximately the same for both the antiferromagnetic and superconducting samples. This clearly demonstrates that RIXS is sensitive to the superexchange J even in doped samples. A positive correlation between J and the maximum of T-c at optimal doping (T-c(max)) is observed. We also measured the x dependence of the d(xy) -> d(x2-y2) and d(xz/yz) -> d(x2-y2) orbital splittings. We infer that the effect of the unresolved d(3z2-r2) -> d(x2 -> y2) excitation on T-c(max) is much smaller than the effect of J. There appears to be dispersion in the d(xy) -> d(x2-y2) peak of up to 0.05 eV. Our fitting furthermore indicates an asymmetric dispersion for the d(xz/yz) -> d(x2-y2) excitation. A peak at similar to 0.8 eV is also observed and attributed to a dd excitation in the chain layer.