An understanding of the physics of strongly correlated multi-orbital electron systems is one of the key ingredients in order to describe a wide range of novel solid state compounds. The complex interplay of the crystal structure with the competition between the localized and the itinerant character of the electrons in a manifestly multi-orbital case is giving rise to highly interesting physical phenomena. By combining the Dynamical Mean Field Theory (DMFT) with the Local Density Approximation (LDA) to Density Functional Theory, a powerful many-body theory is provided to tackle the given problem on a realistic level. Within the LDA+DMFT approach we investigated the multi-orbital system BaVS₃ which is well-known for undergoing three distinct continuous phase transitions with decreasing temperature. In BaVS₃, a first structural transition from a hexagonal to an orthorhombic crystal structure at T_S=240 K is followed by a metal-to-insulator (MI) transition at T_MI=70 K. At around T_X=30 K a final magnetic transition to an incommensurate antiferromagnetic ordered state seems to occur. The highlighted MI transition seems to be accompanied by a charge density wave instability in this partially one-dimensional sulfide. In our study, we concentrate on the MI transition and reveal the importance of the inter-orbital charge transfer between the 3d-orbitals of the V atoms induced by electronic correlations. Using the LDA density of states as an input, with our DMFT investigations we are able to shed light on the underlying mechanism that drives BaVS₃ into the insulating regime.

CPHT-Ecole Polytechnique