Spin and Charge Fluctuations and Lattice Effects on Charge Orders in \alpha-(BEDT-TTF)_2I_3

TL;DR

This study theoretically investigates how spin, charge fluctuations, and electron-phonon interactions influence charge ordering in -(BEDT-TTF)_2I_3, revealing weak lattice effects and the interplay of fluctuations at 3/4 filling.

Contribution

The paper provides a systematic theoretical analysis of lattice effects and fluctuation interactions in -(BEDT-TTF)_2I_3, highlighting the weak lattice influence and the cancellation of spin and charge fluctuation effects.

Findings

Lattice effects on -(BEDT-TTF)_2I_3 are weaker than on similar compounds.

Spin fluctuations are partially canceled by charge fluctuations.

Results align with experimental and mean-field findings.

Abstract

The effects of spin and charge fluctuations and electron-phonon couplings on charge ordering in \alpha-(BEDT-TTF)_2I_3 (BEDT-TTF=bis(ethylenedithio)-tetrathiafulvalence) are investigated theoretically for an anisotropic triangular lattice at 3/4 filling. By the exact-diagonalization method, we have calculated the hole density distributions and the modulations of transfer integrals from high-temperature values as a function of electron-phonon coupling strength. The results clearly show that the lattice effect on \alpha-(BEDT-TTF)_2I_3 is weak compared with that on \theta-(BEDT-TTF)_2RbZn(SCN)_4, as previously found by experiments. This finding, which is also consistent with recent mean-field results, is systematically explained by strong-coupling perturbation theory; the effects of spin fluctuations are partially canceled by charge fluctuations in \alpha-(BEDT-TTF)_2I_3.