Dynamical properties of a strongly correlated model for quarter-filled layered organic molecular crystals

TL;DR

This paper investigates the dynamical properties of an extended Hubbard model relevant to quarter-filled layered organic crystals, revealing a transition from metallic to charge-ordered phases and predicting potential superconductivity near the transition.

Contribution

It provides a detailed analysis of dynamical charge correlations, spectral density, and optical conductivity using Lanczos and large-N techniques, highlighting new insights into charge ordering and superconductivity.

Findings

Transition from metallic to charge-ordered phase as V/t increases

Enhancement of low-frequency spectral weight near transition

Prediction of dxy symmetry superconductivity close to charge order

Abstract

The dynamical properties of an extended Hubbard model, which is relevant to quarter-filled layered organic molecular crystals, are analyzed. We have computed the dynamical charge correlation function, spectral density, and optical conductivity using Lanczos diagonalization and large-N techniques. As the ratio of the nearest-neighbour Coulomb repulsion, V, to the hopping integral, t, increases there is a transition from a metallic phase to a charge ordered phase. Dynamical properties close to the ordering transition are found to differ from the ones expected in a conventional metal. Large-N calculations display an enhancement of spectral weight at low frequencies as the system is driven closer to the charge ordering transition in agreement with Lanczos calculations. As V is increased the charge correlation function displays a plasmon-like mode which, for wavevectors close to (pi,pi), increases in amplitude and softens as the charge ordering transition is approached. We propose that inelastic X-ray scattering be used to detect this mode. Large-N calculations predict superconductivity with dxy symmetry close to the ordering transition. We find that this is consistent with Lanczos diagonalization calculations, on lattices of 20 sites, which find that the binding energy of two holes becomes negative close to the charge ordering transition.