Couplage Spin-Orbite et Interaction de Coulomb dans l’Iridate de Strontium Sr2IrO4 Interplay of Spin-Orbit Coupling and Electronic Coulomb Interactions in Strontium Iridate Sr2IrO4

In this thesis, we were interested in the interplay between the spin-orbit coupling and electronic correlations in condensedmatter physics. The spin-orbit interaction has indeed been found to play a significant role in the properties of a growingvariety of materials, such as the topological band insulators or the iridium-based 5d-transition metal oxides. Particularly,strontium iridate (Sr2IrO4) was recently described as a “spin-orbit driven Mott insulator”: according to this picture, thecooperative interaction between electronic Coulomb interactions and the spin-orbit coupling (ζSO ≈ 0.4 eV) can explainthe insulating state of the compound.We have studied the paramagnetic insulating phase of this material within LDA+DMFT, a method which combinesthe density functional theory in the local density approximation (LDA) with dynamical mean-field theory (DMFT).Sr2IrO4 was found to be a Mott insulator for a reasonable value of the electronic correlations (U = 1.4 eV) once boththe spin-orbit coupling and the lattice distortions were taken into account. Moreover, our results highlight the respectiveroles played by theses two features to reach the Mott insulating state and emphasize that only their acting together mayopen the Mott gap in such a compound.In order to perform this study, the spin-orbit interaction was included in LDA+DMFT – more precisely, to definethe Wannier orbitals on which the local impurity problem is based. The interest of such a technical development goesbeyond the present case of Sr2IrO4 since this “LDA+SO+DMFT implementation” could be also used to take into accountthe electronic correlations in the description of other 5d-transition metal oxides or even topological band insulators. CPhT Ecole Polytechnique – Novembre 2010pastel-00591068,version1-6May2011