Coexistence of distinct charge fluctuations in $\theta$-(BEDT-TTF)$_2$X

TL;DR

This study investigates the complex charge ordering phenomena in an extended Hubbard model on an anisotropic triangular lattice, revealing coexistence of distinct charge fluctuations and their optical signatures.

Contribution

It provides a detailed phase diagram of charge orderings and uncovers coexistence of different charge fluctuations using advanced numerical methods.

Findings

Identified three charge-ordered phases: diagonal, vertical, and three-fold.

Discovered coexistence of diagonal and three-fold charge fluctuations.

Analyzed optical conductivity features for each charge order.

Abstract

Using the Lanczos exact-diagonalization and density-matrix renormalization group methods, we study the extended Hubbard model at quarter filling defined on the anisotropic triangular lattice. We focus on charge ordering (CO) phenomena induced by onsite and intersite Coulomb interactions. We determine the ground-state phase diagram including three CO phases, i.e., diagonal, vertical, and three-fold CO phases, based on the calculated results of the hole density and double occupancy. We also calculate the dynamical density-density correlation functions and find possible coexistence of the diagonal and three-fold charge fluctuations in a certain parameter region where the onsite and intersite interactions compete. Furthermore, the characteristic features of the optical conductivity for each CO phase are discussed.