Charge Ordering in the TMTTF Family of Molecular Conductors

Abstract

Using one-and two-dimensional NMR spectroscopy applied to 13 C spin-labeled (TMTTF)2AsF6 and (TMTTF)2PF6, we demonstrate the existence of an intermediate charge-ordered phase in the TMTTF family of charge-transfer salts. At ambient temperature, the spectra are characteristic of nuclei in equivalent environments, or molecules. Below a continuous charge-ordering transition temperature Tco, the spectra are explained by assuming there are two inequivalent molecules with unequal electron densities. The absence of an associated magnetic anomaly indicates only the charge degrees of freedom are involved and the lack of evidence for a structural anomaly suggests that charge/lattice coupling is too weak to drive the transition.

Ordering phenomena in quasi-one-dimensional organic conductors

“…Below a continuous charge-ordering transition temperature T CO , there is evidence for two inequivalent molecules with unequal electron densities. The absence of an associated magnetic anomaly indicates only the charge degrees of freedom are involved and the lack of evidence for a structural anomaly suggests that chargelattice coupling is too weak to drive the transition (Chow et al 2000).…”

Interaction of magnetic field-dependent Peierls and spin-Peierls ground states in(Per)2[Pt(mnt)Green1, Brooks2, Kuhns3 et al. 2011Phys. Rev. BSelf Cite103100View full textAdd to dashboardCite

“…3 where we compare the features of the NMR experiment with previous electrical transport and magnetization studies of the (P er) 2 …”

“…i) In DA compounds [1], charge transfer can leave the donor with an unpaired spin (leading to a SP transition), while the acceptor is diamagnetic. ii) In D 2 A compounds generally the acceptor chain is a half-filled insulator, and the donor chain is a quarter-filled metal that can undergo sequential CO and SP transitions [2,3]. iii) In the inorganic insulator CuGeO 3 the Cu ++ spin 1/2 chains undergo a SP transition [4].…”

13C NMR study of commensurate antiferromagnetism in (TMTTF)2Br

“…The salts of (TMTTF) 2 AsF 6 and (TMTTF) 2 SbF 6 show CO states below 100 and 157 K, respectively, as well as being in a nonmagnetic insulating state and an antiferromagnetic state, respectively, at low temperature. [9][10][11] The charge imbalance in the disproportionation state of (TMTTF) 2 AsF 6 , ρ = ρ rich − ρ poor , was estimated to be 0.16e by infrared spectroscopy. 12 We suggested a commensurate antiferromagnetic fluctuation in the CO paramagnetic state of (TMTTF) 2 AsF 6 from NMR study.…”