Structural Aspects of the Bechgaard Salts and Related Compounds

Abstract

Structural aspects of the Bechgaard salts (TMTSF)2X and related 2:1 salts, mostly based on the sulfur donors TMTTF and BCPTTF as well as on the hybrid TMDTDSF donor, are considered in relationship with their physical properties. The basic structure of these salts is reviewed with a special emphasize on the dimerization of the organic stack and on the disorder of the anions (X). Then the density waves instabilities driven by the donor stacks are discussed. It is shown in particular that (TMTSF)2PF6 exhibits a mixed 2kF CDW-SDW ground state. The 4kF charge localization phenomena and the 2kF instability of the organic stacks are described in relationship with the structural dimerization and the importance of Coulomb interactions. In the strong charge localization case the spin Peierls instabilities of (TMTTF)2PF6 and of (BCPTTF)2PF6 are more particularly detailed. General aspects of the anion ordering transitions exhibited by salts with non centrosymmetrical anions are pointed out as well as the influence of such transitions on the electronic properties. Finally the relevance of these structural features is briefly discussed by comparing the Bechgaard salts series' of quasi-one dimensional conductors to the family of two dimensional (BEDTTTF)2X conductors

Quantum Monte Carlo study of the pairing symmetry competition in the Hubbard model

“…45 If f -wave is competitive against d-wave even in the absence of strong charge fluctuations, it is likely that f -wave dominates over d-wave in the actual (TMTSF) 2 X, where 2k F CDW actually coexists with SDW. 18,19 For the 2D system, the calculation results (at least for the open shell filling) support presence of attractive interaction in the triplet pairing channel. However, singlet d x 2 −y 2 pairing dominates over all the triplet pairings considered in the present study at the band filling n ≃ 4/3, which corresponds to Sr 2 RuO 4 , in agreement with the FLEX calculation.…”

“…16 A similar proposal has been made by Fuseya et al 17 In fact, the coexistence of 2k F spin and charge density wave has been reported experimentally. 18,19 However, a recent renormalization group study by Fuseya et al 20 has suggested that p-wave pairing dominates over f -wave pairing in quasi-1D systems.…”

Theoretical aspects of charge correlations in θ-(BEDT-TTF)2X

“…Related to this point, a transport experiment has indicated that the repulsive interaction in θ-(BEDT-TTF) 2 MZn(SCN) 4 (M = Cs,Rb) is long-range [44]. In fact, the presence of such a distant interaction has also been pointed out theoretically [45][46][47]49] for quasi-one-dimensional organic compounds (TMTSF) 2 X in the context of coexisting 2k F spin and 2k F charge density waves [50,51] and spin triplet pairing superconductivity for a review e.g. [48,49], [52][53][54][55][56].…”

One Dimensional Organic Superconductors

“…here expressed in units of the reciprocal lattice vector [92,66]. The periodic potential thus created connects two Fermi points along the b direction and opens a gap which doubles the unit cell along that direction.…”

“…of the molecular site energy leading in turn to an additional increase of the preexisting charge gap due to on-site correlations and Umklapp scattering [66] (vide-infra). The case of…”