Laboratoire de Physique Théorique
Toulouse - UMR 5152

In solid state physics, the spin-orbit coupling is commonly thought as a weak relativistic correction" to the Schrödinger equation. However, recent works on strontium rhodate (Sr2RhO4) or iridium-based transition metal oxides (such as strontium iridate, Sr2IrO4) to only name a few [1,2] have shown the significant rearrangements in the band structure which can arise by taking into account both its effect and those of the electronic correlations. Besides, the "spin-orbit driven Mott-insulating" state of Sr2IrO4 was even more striking than 5d-transition metal oxides are expected to be "weakly" correlated.

In this talk, I will investigate the electronic excitations of the paramagnetic phases of Sr2IrO4 and Sr2RhO4 by a combination of the density functional theory within the local density approximation (DFT-LDA) with dynamical mean field theory (DMFT). I will first introduce the LDA+DMFT scheme and its generalization to include spin-orbit coupling. I will then present a scenario entirely from first-principles for both these compounds and discuss the notions of spin-orbital polarization and ordering, while addressing their consequences in these transition-metal oxides [3].

Particularly, it will be shown that the interplay of spin-orbit interactions, structural distortions and Coulomb interactions can suppress spin-orbital fluctuations. As a result, the room temperature phase of Sr2IrO4 is a paramagnetic spin-orbitally ordered Mott insulator. On the contrary, in Sr2RhO4, the effective spin-orbital degeneracy is reduced, but the material remains metallic, due to both, smaller spin-orbit and smaller Coulomb interactions. The obtained spectra are in excellent agreement with photoemission data.

[1] Haverkort et al., Phys. Rev. Lett. 101, 026406 (2008) [2] Kim et al., Phys. Rev. Lett. 101, 076402 (2008) [3] Martins et al., Phys. Rev. Lett. 107, 266404 (2011)