Phase diagram of the correlated quarter-filled-band organic salt series (o-DMTTF)2X(

P. Foury-Leylekian

¹

,

Pascale Auban-Sensier

²

,

C. Coulon

³

et al.

Abstract

The 2:1 family of organic salts (o-DMTTF) 2 X (X = Cl, Br, I) exhibits regular stacks and a high-symmetry structure, which provide a perfect three-quarter-filling-band system allowing a rich phase diagram in the presence of strong electronic correlations. In this paper, we present a detailed study of this series combining complementary experimental techniques such as resistivity, thermopower, electron spin resonance, static magnetic measurements, and x-ray diffraction. In particular, we show that at ambient pressure (o-DMTTF) 2 X with X = Br and Cl undergoes two successive phase transitions setting successively a 4k F charge density and bond order wave order, then a spin-Peierls (SP) ground state. We discuss the symmetry of these phases and its relationship with the transport and magnetic properties. These phases are also followed under pressure by transport experiments, allowing the establishment of a generic phase diagram for this series of salts, where, with the onset of a one-dimensional to three-dimensional deconfinement transition, the 4k F order vanishes and the SP ground state transforms into a Peierls one. Interestingly, this phase diagram differs significantly from the one previously reported in other three-quarter-filled systems such as (TMTTF) 2 X and δ-(EDT-TTF-CONMe 2 ) 2 X.

Structural properties of solid solutions of the non‐dimerized, 3/4‐filled conductors (o‐DMTTF)2X (X = Cl, Br, I)

“…As shown in Ref. [8] for pure samples, the location of the maximum of the linewidth roughly corresponds to the charge/bond order phase transition. The data shown in Fig.…”

“…4 anion substitution, at variance with the in-plane a (and b) parameters which extend with increasing anion size. This behavior indicates that upon anion substitution, the columns of conducting mixed-valence o-DMTTF are pushed apart from each other with larger anions, while the intra-stack interactions are essentially the same, as illustrated by the similar room temperature conductivities of the three salts [8].…”

“…These salts crystallize in the quadratic system, space group I-42d [6,7]. A combination of experimental techniques: resistivity, thermopower, ESR, static magnetic measurements, and X-ray diffraction, recently allowed us to obtain a consistent picture of the low temperature ground states stabilized in this family [8]. A generic phase diagram was proposed to unify the various results obtained.…”

Charge ordering in low dimensional organic conductors: Structural aspects

“…The material is a 1D metal at atmospheric pressure, P atm . The (T, P) phase diagram [11] reveals that Cl and Br salts undergo two successive phase transitions at low pressure. Above these transitions, the Cl and Br salts exhibit 4k F and 2k F 1D structural instabilities.…”

Theoretical Studies on Phase Transitions in Quasi-One-Dimensional Molecular Conductors

“…Here, zV ⊥ correspond to the inverse of P ; the effect of P acts strongly on transfer integrals, therefore the "effective" Coulomb interaction becomes smaller. Now, several Q1D compounds without dimerization have been synthesized where a CO transition is suggested, such as (o-DMTTF) 2 Br [55] and (EDT-TTF-CONMe 2 ) 2 X [X = AsF 6 and Br] [56,57]. On the other hand, materials known from early days such as the compounds showing SP transition, MEM-(TCNQ) 2 and (BCPTTF) 2 X (X = PF 6 , AsF 6 ) [58][59][60], might be interesting to revisit with renewed understandings.…”