Reentrant field-induced spin-density-wave transitions

The metallic transport of (TMTSF)2X organic conductors close to the superconducting phase

Comparing resistivity data of the quasi-one-dimensional superconductors (TMTSF)2PF6 and (TMTSF)2ClO4 along the least conducting c(⋆)-axis and along the high conductivity a-axis as a function of temperature and pressure, a low temperature regime is observed in which a unique scattering time governs the transport along both directions of these anisotropic conductors. However, the pressure dependence of the anisotropy implies a large pressure dependence of the interlayer coupling. This is in agreement with the results of first-principles density functional theory calculations implying methyl group hyperconjugation in the TMTSF molecule. In this low temperature regime, both materials exhibit for ρ(c) a temperature dependence aT + bT(2). Taking into account the strong pressure dependence of the anisotropy, the T-linear ρ(c) is found to correlate with the suppression of the superconducting Tc, in close analogy with ρ(a) data. This work reveals the domain of existence of the three-dimensional coherent regime in the generic (TMTSF)2X phase diagram and provides further support for the correlation between T-linear resistivity and superconductivity in non-conventional superconductors.

Competing phases in the high field phase diagram of (TMTSF)(2)ClO(4)

A model is presented for the high field phase diagram of (TMTSF)(2)ClO(4), taking into account the anion ordering, which splits the Fermi surface into two bands. For strong enough field, the largest metal spin density wave critical temperature corresponds to the N=0 phase, which originates from two intraband nesting processes. At lower temperature, the competition between these processes puts at disadvantage the N=0 phase vs the N=1 phase, which is due to interband nesting. A first order transition then takes place from the N=0 to N=1 phase. We ascribe to this effect the experimentally observed phase diagrams.