Magnetic resonant x-ray scattering in KCuF3 -: art. no. 064425

We study the magnetic resonant x-ray scattering (RXS) spectra around the K edge of Cu in KCuF3 on the basis of an ab initio calculation. We use the full-potential linearlized augmented plane wave method in the local density approximation (LDA)+U scheme, and introduce the lattice distortion as inputs of the calculation. We obtain finite intensity on magnetic superlattice spots by taking account of the spin-orbit interaction (SOI). No intensity appears without the SOI, indicating that the intensity arises not from the spin polarization but from the orbital polarization concerning complex wave functions in 4p states. The present calculation reproduces well the experimental spectra as functions of photon energy and of azimuthal angle. We also calculate the RXS intensity on orbital superlattice spots. It is found that the intensity increases with increasing Jahn-Teller distortion. The spectra arise from the orbital polarization concerning real wave functions p(x), p(y), and p(z). They remain nearly the same in the nonmagnetic state given by the simple LDA, in which the orbital order constructed in the 3d states is much smaller. This strongly suggests that the intensity on orbital spots is mainly controlled by the lattice distortion, not by the 3d orbital order itself.