How to read between the lines of electronic spectra: the diagnostics of fluctuations in strongly correlated electron systems

While calculations and measurements of single-particle spectral properties often offer the most direct route to study correlated electron systems, the underlying physics may remain quite elusive, if information at higher particle levels is not explicitly included. Here, we present a comprehensive overview of the different approaches which have been recently developed and applied to identify the dominant two-particle scattering processes controlling the shape of the one-particle spectral functions and, in some cases, of the physical response of the system. In particular, we will discuss the underlying general idea, the common threads and the specific peculiarities of all the proposed approaches. While all of them rely on a selective analysis of the Schwinger-Dyson (or the Bethe-Salpeter) equation, the methodological differences originate from the specific two-particle vertex functions to be computed and decomposed. Finally, we illustrate the potential strength of these methodologies by means of their applications the two-dimensional Hubbard model, and we provide an outlook over the future perspective and developments of this route for understanding the physics of correlated electrons.

Automated summary

This article provides a comprehensive overview of different methodologies developed to identify the dominant two-particle scattering processes controlling the shape of single-particle spectral functions and the physical response of correlated electron systems. The approaches rely on selective analysis of the Schwinger-Dyson or Bethe-Salpeter equations, with methodological differences originating from the specific two-particle vertex functions to be computed and decomposed. The potential strength of these methodologies is illustrated through applications to the two-dimensional Hubbard model, offering insights for future developments in understanding the physics of correlated electrons.