Spectral shift technique for strongly correlated lattice fermions

TL;DR

This paper introduces a spectral shift technique for strongly correlated lattice fermions that improves the expansion around a quasiparticle spectrum by integrating out mean-field paths, enhancing accuracy in kinetic energy calculations.

Contribution

It develops a novel strong-coupling diagrammatic method that incorporates kinetic effects more effectively by integrating out mean-field paths before expansion.

Findings

Method aligns well with exact results

Enhances the accuracy of kinetic energy representation

Provides a better starting point for diagrammatic expansions

Abstract

We present a development of strong-coupling diagrammatic techniques which relies on integrating out mean-field-like paths prior to conducting the expansion. This makes it possible to expand around a state with a quasiparticle spectrum that takes into account all kinetic effects that do not explicitly depend on nonlocal correlations. These paths contribute most of the kinetic energy in correlated systems, and so this protocol provides a starting point for the expansion that more closely resembles the full theory. Comparisons to existing exact results clearly confirm this.