Fluctuation diagnostics of the electron self-energy: Origin of the pseudogap physics

TL;DR

This paper introduces a method to identify the dominant physical processes affecting low-energy spectral functions in correlated electron systems, clarifying the origin of the pseudogap phenomenon.

Contribution

It presents a novel classification technique based on the equation of motion for the electron self-energy, applied to distinguish the roles of charge, spin, and pairing fluctuations in pseudogap physics.

Findings

Spin fluctuations cause the pseudogap in the repulsive Hubbard model.

d-wave pairing fluctuations are less influential in pseudogap formation.

The method clarifies the physical origin of spectral features in correlated systems.

Abstract

We demonstrate how to identify which physical processes dominate the low-energy spectral functions of correlated electron systems. We obtain an unambiguous classification through an analysis of the equation of motion for the electron self-energy in its charge, spin and particle-particle representations. Our procedure is then employed to clarify the controversial physics responsible for the appearance of the pseudogap in correlated systems. We illustrate our method by examining the attractive and repulsive Hubbard model in two-dimensions. In the latter, spin fluctuations are identified as the origin of the pseudogap, and we also explain why $d-$wave pairing fluctuations play a marginal role in suppressing the low-energy spectral weight, independent of their actual strength.