Determining the depth distribution of RIXS excitations through standing-wave excitation

The interface properties of oxide heterostructures exhibit novel physical effects that are due to the coupling of the charge, spin and orbital states. Resonant inelastic x-ray scattering (RIXS) is a powerful technique for studying in an element- and orbital specific way for charge transfer, $d$-$d$, magnetic, and other excitations, but it lacks depth resolution. Here we combine soft x-ray RIXS at the Cu L3 resonance with SW excitation to provide depth resolution and interface sensitivity, with first application to superconductor/half-metallic ferromagnetic multilayers of (La$_{1.85}$Sr$_{0.15}$CuO$_{4})_{n}$/(La$_{0.66}$Sr$_{0.33}$MnO$_{3})_{m}$ (LSCO/LSMO). The standing wave was swept along the direction normal to the sample surface by varying the incidence angle around the multilayer Bragg angle, producing ``rocking curves'' (RCs) of the intensities of individual excitations. The RCs of RIXS excitations are significantly different for samples grown on SrO- and TiO$_{2}$- terminated SrTiO$_{3}$, indicating different depth distributions. For the dd excitations of the TiO$_{2}$-terminated sample, the z$^{2}$ orbital excitations arise from the interface, while the xy and xz/yz orbital excitations arise from the bulk region of the LSCO layer.