Phase diagram of quarter-filled band organic salts, [EDT-TTF-CONMe2]2X, X = AsF6 and Br

TL;DR

This study maps the pressure-temperature phase diagram of quarter-filled organic salts [EDT-TTF-CONMe2]2X, revealing charge ordering, insulating behavior, and phase transitions driven by pressure, with implications for understanding correlated 1/4-filled conductors.

Contribution

It provides the first detailed phase diagram of these salts, highlighting charge order stability and phase transitions distinct from related dimerized compounds.

Findings

Charge ordered state confirmed by 13C NMR.

Insulating behavior dominates at low pressure.

Non-magnetic insulating phase appears under pressure.

Abstract

An investigation of the P/T phase diagram of the quarter-filled organic conductors, [EDT-TTF-CONMe2]2X, is reported on the basis of transport and NMR studies of two members, X=AsF6 and Br of the family. The strongly insulating character of these materials in the low pressure regime has been attributed to a remarkably stable charge ordered state confirmed by 13C NMR and the only existence of 1/4 Umklapp e-e scattering favoring a charge ordering instead of the 1D Mott localization seen in (TM)2X which are quarter-filled compounds with dimerization. A non magnetic insulating phase instead of the spin density wave state is stabilized in the deconfined regime of the phase diagram. This sequence of phases observed under pressure may be considered as a generic behavior for 1/4-filled conductors with correlations.