Excitonic dispersion of the intermediate-spin state in LaCoO3 revealed by resonant inelastic X-ray scattering

Abstract: In this talk, we discuss two recent studies using resonant inelastic X-ray scattering (RIXS) [1,2].

First, we present Co L-edge RIXS study on LaCoO3 [1]. We observe excitations with sizable dispersion that we identify as intermediate-spin (IS) states. Theoretical calculations that treat the IS states as mobile excitons propagating on the low-spin background support the interpretation. The present result shows that mobility substantially reduces the energy of IS excitations in a part of the Brillouin zone, which makes them important players in the low-energy physics of LaCoO3 together with immobile high-spin excitations.
Second, we present a theoretical study of Cu L-edge RIXS of LaCuO3 and NaCuO2, typical high-valence transition-metal oxides, using a theoretical framework based on the local-density approximation + dynamical mean-field theory [3]. This study is motivated by recent experiments, revealing unusual coexistence of bound and continuum excitations in L-edge RIXS spectra [4]. We analyze in detail the behavior of the fluorescence-like feature and show how it is connected to the details of electronic and crystal structure. On the studied compounds we demonstrate how material details determine whether electron-hole continuum can be excited in the L-edge RIXS process.

[1] R.-P. Wang, A. Hariki, A. Sotnikov, F. Frati, J. Okamoto, H.-Y. Huang, A. Singh, D.-J. Huang, K. Tomiyasu, C.-H. Du, J. Kunes, and F. M. F. de Groot, arXiv:1712.04906 (2017).
[2] A. Hariki, M. Winder, and J. Kunes, arXiv:1803.03820 (2018)
[3] A. Hariki, T. Uozumi, and J. Kunes, Phys. Rev. B 96. 045111 (2017)
[4] V. Bisogni, S. Catalano, R. J. Green, M. Gibert, R. Scherwitzl, Y. Huang, V. N. Strocov, P. Zubko, S. Balandeh, J.-M. Triscone, G. Sawatzky, T. Schmitt, Nat Commun. 7. 13017 (2016)