Kinks and Mid-Infrared Optical Conductivity from Strong Electron Correlation

TL;DR

This paper uses cellular dynamical mean-field theory to study the 2D Hubbard model, revealing a kink in spectral dispersion and a mid-infrared peak in optical conductivity linked to strong electron correlations and the pseudogap.

Contribution

It demonstrates a direct connection between mid-infrared absorption features and specific plaquette states with d$_{x^2-y^2}$ symmetry in the Hubbard model.

Findings

Identifies a kink in spectral function dispersion.

Detects a mid-infrared absorption peak in optical conductivity.

Links the mid-IR feature to a specific plaquette state with d$_{x^2-y^2}$ symmetry.

Abstract

We compute the one-particle spectral function and the optical conductivity for the 2-d Hubbard model on a square lattice. The computational method is cellular dynamical mean-field theory (CDMFT) in which a 4-site Hubbard plaquette is embedded in a self-consistent bath. We obtain a `kink' feature in the dispersion of the spectral function and a mid-infrared (mid-IR) absorption peak in the optical conductivity, consistent with experimental data. Of the 256 plaquette states, only a single state which has d$_{x^2-y^2}$ symmetry contributes to the mid-IR, thereby suggesting a direct link with the pseudogap. Local correlations between doubly and singly occupied sites which lower the kinetic energy of a hole are the efficient cause of this effect.