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It has been recognized that both spin and orbital degrees of freedom are the key to understanding the physics of iron pnictides. Theoretical calculations within the random-phase approximation for a five-orbital Hubbard model have nicely explained spin excitations observed by inelastic neutron scattering experiments for antiferromagnetic (AF) phase [1]. For charge dynamics, the in-plane anisotropy of optical conductivity has been explained by taking into account orbital characters of interband excitations [2]. In order to clarify the interplay of spin, charge, and orbital degrees of freedom in the energy and momentum spaces, we propose resonant inelastic x-ray scattering (RIXS) tuned for Fe L3 edge [3]. In the AF phase, we find that the magnon excitations predominantly composed of single orbital component appear with a weak intensity as compared with orbital excitations lying just above the magnon excitations. The dominant orbital excitations are found to be accompanied by the spin-flip process, producing composite excitations of the coupled orbital-spin degrees of freedom. We also predict the polarization and momentum dependence of the Fe L3-edge RIXS. [1] E. Kaneshita and T. Tohyama, Phys. Rev. B 82, 094441 (2010). [2] K. Sugimoto, E. Kaneshita, and T. Tohyama, J. Phys. Soc. Jpn. 80, 033706 (2011). [3] E. Kaneshita, K. Tsutsui, , and T. Tohyama, Phys. Rev. B 84, 020511(R) (2011). |
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