Pyrochlore iridates: Electronic and magnetic structures, x-ray magnetic circular dichroism, and resonant inelastic x-ray scattering
V. N. Antonov, L. V. Bekenov, D. A. Kukusta
Abstract
We have investigated the electronic and magnetic properties of the pyrochlore iridates ${\mathrm{Y}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$, ${\mathrm{Pr}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$, and ${\mathrm{Eu}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ within the density-functional theory (DFT) using the generalized gradient approximation with taking into account strong Coulomb correlations ($\mathrm{GGA}+U$) in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. The x-ray absorption spectra (XAS) and x-ray magnetic circular dichroism (XMCD) at the Ir ${L}_{2,3}$, Pr ${L}_{2,3}$, Pr ${M}_{4,5}$, and O $K$ edges in the pyrochlore iridate ${\mathrm{Pr}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ have been investigated theoretically from first principles. The calculated results are in good agreement with experimental data. We have also investigated theoretically the resonant inelastic x-ray scattering (RIXS) spectra at the Ir ${L}_{3}$ edge in the pyrochlore iridates ${\mathrm{R}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ (R = Y, Pr, and Eu). We have found that these materials exhibit qualitatively similar excitation spectra. The experimentally measured RIXS spectra of all three compounds in addition to the elastic scattering peak at 0 eV possess sharp features below 2 eV corresponding to transitions within the Ir ${t}_{2g}$ levels, and a strong intense peak stretching from 2.5 to 5 eV that according to the calculations corresponds to $d\text{\ensuremath{-}}d$ transitions between the Ir ${t}_{2g}$ and ${e}_{g}$ manifolds. We have found that the double peak at low energy can be assigned to local excitations between the filled ${J}_{\text{eff}}=1/2$ and empty ${J}_{\text{eff}}=1/2$ manifolds; the latter states are split into two subbands.