Electronic properties of Fabre charge-transfer salts under various temperature and pressure conditions

TL;DR

This study uses density functional theory to analyze how temperature and pressure influence the electronic properties of Fabre charge-transfer salts, revealing trends towards increased two-dimensionality and the effects of Coulomb interactions on charge and magnetic order.

Contribution

It provides new experimental crystal structures under various conditions and links electronic behavior trends to the complex phase diagram of these salts.

Findings

Decreasing temperature and increasing pressure increase two-dimensionality.

Charge order is strongly affected by inter-site Coulomb interactions.

Magnetic order is only weakly influenced and both orders diminish under higher pressure.

Abstract

Using density functional theory, we determine parameters of tight-binding Hamiltonians for a variety of Fabre charge transfer salts, focusing in particular on the effects of temperature and pressure. Besides relying on previously published crystal structures, we experimentally determine two new sets of structures; (TMTTF)$_2$SbF$_6$ at different temperatures and (TMTTF)$_2$PF$_6$ at various pressures. We find that a few trends in the electronic behavior can be connected to the complex phase diagram shown by these materials. Decreasing temperature and increasing pressure cause the systems to become more two-dimensional. We analyze the importance of correlations by considering an extended Hubbard model parameterized using Wannier orbital overlaps and show that while charge order is strongly activated by the inter-site Coulomb interaction, the magnetic order is only weakly enhanced. Both orders are suppressed when the effective pressure is increased.