First direct observation of single magnons by oxygen K-edge RIXS on iridates.

Iridates are 5d TM oxides which have called much attention because of the observation of novel insulating and correlated metallic ground states as well as for the fascinating theoretical proposals envisioned (superconductivity and unusual topological phases) for them. The key ingredients of iridates are: Ir 5d band behavior, strong Spin-Orbit coupling (SOC) and moderate electronic correlations. Iridates of the Srn+1IrnO3n+1 (n=1,2,...) (Ruddlesden-Popper) series display a metal to insulator transition as the number (n) of IrO2 of layers is reduced. Resonant Inelastic X-ray Scattering (RIXS) is an established technique which can provide invaluable information on the electronic and low energy sector of the Hamiltonian by probing elementary excitations in solids. By measuring the O K-edge RIXS response of the insulating members of the Ruddlesden-Popper series (n=1 and 2), we identified and registered the momentum dispersion of magnetic modes. The energy of the low energy modes correlates well with that of single magnons observed by Ir L3 RIXS [6]. This suggests that the magnetic excitations observed in insulating iridates by O K-edge RIXS correspond not to bi-magnons (as in cuprates) but to single magnons. This interpretation was recently confirmed by theoretical work done by Kim and van der Brink, thus our work is the first experimental verification of a novel selection rule for magnetic excitations during indirect RIXS processes for systems with strong SOC. Additionally, an excitation with marked Ir5d character was also identified in all the O K-edge RIXS spectra of the studied iridates, including correlated metallic Bi2Ir2O. While the spectral shape of this excitation seems to be related to the strength of electronic correlations in the system, its energy again seems to correlate well with that of the so called Spin-Orbit exciton also observed by Ir L3 RIXS on insulating iridates.

Participante: Paul Olalde-Velasco

Institución: Paul Scherrer Institut, Suiza

Fecha y hora: Este evento terminó el Miércoles, 14 de Enero de 2015