Correlation of the superconducting critical temperature with spin and orbital excitations in (Ca_xLa_(1-x))(Ba_(1.75-x)La_(0.25+x))Cu_3O_y as measured by resonant inelastic x-ray scattering

摘要

Electronic spin and orbital (dd) excitation spectra of (Ca_xLa_(1-x))(Ba_(1.75-x)La_(0.25+x))Cu_3O_y samples are measured 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 × due to subtle variations in the lattice constants, while crystal symmetry and disorder as measured by linewidths are × 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 (r_c~(max)) is observed. We also measured the x dependence of the d_(xy)→ d_(x~2-y~2) and d_(xz/yz)→d_(x~2-y~3) orbital splittings. We infer that the effect of the unresolved d_(3z~2-r~2) → d_(x~2-y~2) excitation on T_c~(max) is much smaller than the effect of J. There appears to be dispersion in the d_(xy) → d_(x~2-y~2) peak of up to 0.05 eV. Our fitting furthermore indicates an asymmetric dispersion for the d_(xz/yz) → d_(x~2-y~2) excitation. A peak at ～0.8 eV is also observed and attributed to a dd excitation in the chain layer.