Beyond Gaussian pair fluctuation theory for strongly interacting Fermi gases

TL;DR

This paper develops a new theoretical framework for strongly interacting Fermi gases that goes beyond the traditional ladder approximation, providing accurate predictions of their equation of state in three and two dimensions.

Contribution

It introduces an alternative diagram reorganization method that accounts for the decreasing effective interaction above three dimensions, improving upon existing strong coupling theories.

Findings

Excellent agreement with experimental data above 0.5TF

Provides accurate equation of state for 2D and 3D strongly interacting fermions

Offers a new approach to many-body diagrammatic expansions in strongly correlated systems

Abstract

Interacting Fermi systems in the strongly correlated regime play a fundamental role in many areas of physics and are of particular interest to the condensed matter community. Though weakly inter- acting fermions are understood, strongly correlated fermions are difficult to describe theoretically as there is no small interaction parameter to expand about. Existing strong coupling theories rely heavily on the so-called many-body T-matrix approximation that sums ladder-type Feynman diagrams. Here, by acknowledging the fact that the effective interparticle interaction (i.e., the vertex function) becomes smaller above three dimensions, we propose an alternative way to reorganize Feynman diagrams and develop a theoretical framework for interacting Fermi gases beyond the ladder approximation. As an application, we solve the equation of state for three- and two-dimensional strongly interacting fermions and find excellent agreement with experimental [Science 335, 563 (2012)] and other theoretical results above the temperature 0.5TF .