Antiferromagnetic Phases of One-Dimensional Quarter-Filled Organic Conductors

TL;DR

This paper theoretically investigates the magnetic structures of antiferromagnetic phases in quasi-one-dimensional organic conductors at zero temperature, highlighting the effects of Coulomb interactions and charge disproportionation.

Contribution

It introduces a mean field model considering on-site and nearest-neighbor Coulomb interactions to explain magnetic phases and charge ordering in organic conductors, aligning with experimental observations.

Findings

Nearest-neighbor Coulomb interaction causes charge disproportionation.

Antiferromagnetic phase in (TMTTF)$_2$X matches experimental data.

Predicted similar spin structure in (DI-DCNQI)$_2$Ag.

Abstract

The magnetic structure of antiferromagnetically ordered phases of quasi-one-dimensional organic conductors is studied theoretically at absolute zero based on the mean field approximation to the quarter-filled band with on-site and nearest-neighbor Coulomb interaction. The differences in magnetic properties between the antiferromagnetic phase of (TMTTF)$_2$X and the spin density wave phase in (TMTSF)$_2$X are seen to be due to a varying degrees of roles played by the on-site Coulomb interaction. The nearest-neighbor Coulomb interaction introduces charge disproportionation, which has the same spatial periodicity as the Wigner crystal, accompanied by a modified antiferromagnetic phase. This is in accordance with the results of experiments on (TMTTF)$_2$Br and (TMTTF)$_2$SCN. Moreover, the antiferromagnetic phase of (DI-DCNQI)$_2$Ag is predicted to have a similar antiferromagnetic spin structure.