Electron spin resonance studies on the organic linear-chain compounds(TMTCF)2X (C=S

Abstract

temperature. In contrast to the selenium analogs TMTSF which are one-dimensional metals, the sulfur salts are semiconductors with localized spins on the TMTTF dimers. Taking into account the thermal expansion of the crystals at high temperature (TϾ20 K) the ESR intensity of all sulfur compounds can be described as a spin-1/2 antiferromagnetic Heisenberg chain with exchange constants 420рJ р500 K. Although the TMTSF compounds are one-dimensional organic metals down to 10 K, the temperature dependence of the spin susceptibility can also be described within the framework of the Hubbard model in the limit of strong Coulomb repulsion with JϷ1400 K. By modeling (TMTTF) 2 ClO 4 as an alternating spin chain, the change of the alternation parameter at the first-order phase transition (T AO ϭ72.5 K) indicates a tetramerization of the chain. (TMTTF) 2 PF 6 undergoes a spin-Peierls transition at T SP ϭ19 K which can be well described by Bulaevskii's model with a singlet-triplet gap ⌬ (0)ϭ32.3 K. We find evidence of antiferromagnetic fluctuations at temperatures well above the magnetic ordering in (TMTTF) 2 Br, (TMTSF) 2 PF 6 , and (TMTSF) 2 AsF 6 which follow the critical behavior expected for three-dimensional ordering. (TMTTF) 2 PF 6 and (TMTTF) 2 Br show one-dimensional lattice fluctuations.

Spin-charge separation in quasi one-dimensional organic conductors

“…As well as the Mott insulating state, spin Peierls, antiferromagnetic insulator, spin-density-wave, and superconductivity which occur when the coupling between the stacks is increased, in addition the metallic state changes its behavior, going from a Luttinger liquid to a Fermi liquid. This can be nicely seen in electronic properties like the c-axis resistivity (Moser et al 1998) or the optical conductivity (Dressel et al 1996); spin dynamics, on the other hand, does not show any fundamental change going from TMTTF to TMTSF except that the spins are less localized (Dumm et al 2000). Most recently thermal transport also indicated that the charge degrees of freedom behave in a totally different way from the spin degrees of freedom (Lorenz et al 2002).…”

“…In order to investigate the spin degrees of freedom, detailed studies of the electron spin resonance (ESR) were performed on most of the TMTCF salts (Dumm et al 2000). The integrated absorption is proportional to the spin susceptibility; at high temperatures c(T) of the (TMTTF) 2 X -compounds (Fig.…”

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

“…The values of the intrachain hopping parameters in our work are consistent with those found for similar systems in previous experimental and theoretical investigations. [27][28][29][30][31][32][33] Missing in those previous studies is a thorough analysis of the intrachain dimerization as well as the interchain hopping parameters.…”

“…At pressures above P = 1.3 GPa, (TMTTF) 2 PF 6 is known experimentally to become metallic, and at low temperatures undergoes a spin-density wave transition. 32,37 Figure 9(b) shows how the dimensionality and bandwidth of (TMTTF) 2 PF 6 varies with pressure. We observe the expected trend of increasing bandwidth under pressure (forcing the TMTTF molecules closer together, increasing their intermolecular interactions).…”

Scaling behavior of the longitudinal and transverse transport in quasi-one-dimensional organic conductors

“…In the b direction the distance of the stacks is comparable to the van der Waals radii. Most prominent findings are the reduced density of states at the Fermi energy as indicated by photoemission spectroscopy, 15 the c-axis transport investigated by pressure-dependent dc resistivity, 16 the scaling behavior in the optical conductivity, 17 the Hall effect, 18,19 and finally indications of spin-charge separation by the similarity in the spin dynamics 20 and thermal conductivity 21 for TMTSF and TMTTF salts although the electronic transport is very different; for a review see Ref. 22.…”