SKM 2023 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 65: Correlated Electrons: Other Theoretical Topics

TT 65.4: Vortrag

Freitag, 31. März 2023, 10:15–10:30, HSZ 204

Breakdown of the many-electron perturbation expansion beyond particle-hole symmetry — •Herbert Eßl, Matthias Reitner, and Alessandro Toschi — Institute of Solid State Physics, TU Wien

The breakdown of the self-consistent perturbation theory for many-electron systems has several physical and formal manifestations. Among the latter, one of the most studied is the divergence of two-particle irreducible vertex functions. Hitherto most investigations of the divergences appearing in the irreducible vertex functions of many-electron systems have been restricted to the particle hole symmetric cases and the calculations were performed at finite temperatures. This work is a first step beyond such restrictions. To this aim we investigate the two particle properties of the Hubbard Atom, both for positive (repulsive) and negative (attractive) on-site interaction. As a main result a universal phase-diagram of vertex divergences, valid for arbitrary (finite) temperatures, has been determined. Using this result as a "compass", the T=0 limit has been investigated, in order to unveil possible connections between the vertex divergences and the validity or the violation of the Luttinger Theorem. We also study the convergence of the self-consistent perturbation series beyond the particle-hole symmetry condition, determining specific constraints for the convergence of the series to the physical solution at arbitrary electronic densities.