Benjamin BACQ-LABREUIL

PhD Student

Research group: Condensed matter

Advisor: Silke Biermann

Thesis: "Correlated Electron Materials: Many-body perturbation theory and dynamical mean field techniques for realistic multi-orbital models"

Research interests

- Correlated systems
- Dynamical Mean Field Theory
- Many-Body perturbation Theory
- Multi-orbitals systems

Abstract 

The current thesis aims at understanding long-range screening phenomena arising from non-local interactions in multi-orbital extended Hubbard models. To this effect, we will study multi-orbital models with non-local interactions within GW+DMFT and related many-body theoretical schemes.The goal is threefold: 1) develop a systematic understanding of the effects of long-range interactions in multi-orbital Hubbard models, 2) develop the needed numerical techniques within a GW+DMFT formalism and beyond, 3) use these tools to understand satellite structures and screening phenomena in real materials (in particular, in late transition metal oxides). Screening phenomena induce spectral weight transfers in the spectral properties of the systems.This weight transfer is directly linked to a mass enhancement of the electrons, and is essential for getting closer to the experimental results. Several applications to real materials have been done : for SrVO3 and BaFe2As2. However, except for SrVO3, none of the multi-orbital calculations has attempted full self-consistency over the DMFT and GW cycles, and –intriguingly – self-consistency in SrVO3 leads to surprisingly weakly correlated states. A more systematic understanding at the model level, that can then later be transcribed to the case of realistic materials, is urgently needed.Taking into account several orbitals is essential not only because of the large number of materials with degenerate correlated shells. It is also a key step in including “uncorrelated” ligand orbitals into the description. In particular in late transition metal oxides such as cuprates or nickelates, the latter may become crucial for a true understanding and quantitative description.