Dispersive magnetic and electronic excitations in iridate perovskites probed by oxygen K -edge resonant inelastic x-ray scattering

Abstract

Resonant inelastic x-ray scattering (RIXS) experiments performed at the oxygen K edge on the iridate perovskites Sr 2 IrO 4 and Sr 3 Ir 2 O 7 reveal a sequence of well-defined dispersive modes over the energy range up to ∼0.8 eV. The momentum dependence of these modes and their variation with the experimental geometry allows us to assign each of them to specific collective magnetic and/or electronic excitation processes, including single and bimagnons, and spin-orbit and electron-hole excitons. We thus demonstrate that dispersive magnetic and electronic excitations are observable at the O K edge in the presence of the strong spin-orbit coupling in the 5d shell of iridium and strong hybridization between Ir 5d and O 2p orbitals, which confirm and expand theoretical expectations. More generally, our results establish the utility of O K-edge RIXS for studying the collective excitations in a range of 5d materials that are attracting increasing attention due to their novel magnetic and electronic properties. Especially, the strong RIXS response at O K edge opens up the opportunity for investigating collective excitations in thin films and heterostructures fabricated from these materials. DOI: 10.1103/PhysRevB.97.041102 Characterizing the elementary excitations in correlated electron systems is an essential prerequisite for obtaining a complete understanding of the underlying electronic interactions and therefore crucial for revealing the origin of emergent phases [1,2]. Resonant inelastic x-ray scattering (RIXS) has become established in the past decade as a powerful tool for studying the momentum dependence of electronic and magnetic excitations [2]

High-resolution resonant inelastic x-ray scattering study of the electron-phonon coupling in honeycomb α−Li2IrO3

“…This includes a sharp feature at 0.46 eV which originates from coupling between the electron-hole excitation of the j eff = 1/2 band, and the "spin-orbit exciton" close to the optical absorption edge [34]. The fact that they can be seen at the O K-edge is due to the aforementioned Ir-O hybridization, with similar behavior observed previously for the perovskite iridates [32].…”

“…In Sr 2 IrO 4 and Sr 3 Ir 2 O 7 , the observed splitting of peak E 1 was attributed to selective coupling to the in-plane or apical oxygen atoms [32]. This could be clearly observed from the polarization dependence of the XAS spectra.…”

Oxygen states in La- and Rh-doped Sr2IrO4 probed by angle-resolved photoemission and O K -edge resonant inelastic x-ray scattering

“…There have been many ARPES studies of Sr 2 IrO 4 , undoped 1 and doped [8][9][10] , but they focused on the Ir states near the Fermi level. Similarly, previous RIXS studies, both at the Ir L edge [11][12][13] and O K edge 14,15 , focused on the low energy excitations.…”

“…Previous studies have mainly focused on the low energy Raman structures, visible both in Ir L 3/2 edge RIXS spectra 12,13 and O K edge RIXS spectra 14,15 . These are spin-orbit exciton (feature labelled E at 0.65 eV energy loss in the Fig.4b) and single-and bi-magnon excitations at about 100 meV, and 150 meV, respectively, visible in our data as a shoulder near the elastic peak.…”

Spin-Orbital Excitations in Ca2RuO4 Revealed by Resonant Inelastic X-Ray Scattering

“…However, the full manifold of the low-lying spin-orbital excitations of Ca 2 RuO 4 has not yet been observed. The possibility to detect Ru d-orbital excitations through the oxygen K-edge [18,19], offers a unique opportunity in the case of ruthenates, where direct L-edge RIXS is not yet available for high-resolution measurements. Moreover, spin-orbital excitations are mostly inaccessible to neutron scattering.…”