Electronic states of LaCoO$_3$: Co K-edge and La L-edge X-ray absorption studies

Abstract

Room temperature Co K- and La L-edges X-ray absorption studies have been carried out on LaCoO$_3$. Experimental near edge structures have been analysed by theoretical LDA+U density of states (DOS) and multiple scattering (MS) calculations. Use of both MS and DOS calculations yield additional information about hybridization of the states of central atom with neighbouring atoms responsible for producing the near edge structures. Absorption processes at Co K-, La L1-, L2-, and L3-edges have been attributed to electronic transitions from Co 1s to Co 4p, La 2s to La 6p, La 2p$_{1/2}$ to La 5d, and La 2p$_{3/2}$ to La 5d, respectively. All the pre-edge and post-edge features including the shape of the main absorption edge have been generated by taking the convolution of the calculated DOS, indicating that single particle approximation is sufficient to express all experimentally observed major structures. Two pre-edge structures observed in Co K-edge spectrum are attributed to Co 1s to e$_g^{\uparrow}$ and e$_g^$\downarrow}$ quadrupole transitions in contrast to earlier identification of the same to Co 1s to t$_{2g}$ and e$_g$ transitions. The influence of La 6p states on the Co 4p states is such that the inclusion of La atoms in the MS calculations is necessary to generate post-edge structures in Co K-edge spectrum. The importance of the hybridization of O 2p state with La 6p and 5d in the L-edge absorption processes has also been discussed. 10% contribution of quadrupole channel has been estimated in La L-edges.