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

TL;DR

This paper reviews advanced methods for analyzing two-particle scattering processes to better understand the physics of strongly correlated electron systems, especially through spectral functions and response properties.

Contribution

It provides a comprehensive overview of recent approaches based on analyzing the Schwinger-Dyson and Bethe-Salpeter equations to identify dominant scattering processes.

Findings

Methods successfully applied to the 2D Hubbard model

Enhanced understanding of spectral function shaping

Potential for future developments in correlated electron physics

Abstract

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.