Basic considerations on broken-symmetry states of organic superconductors

Abstract

In this brief account, we shall review the different mechanisms giving rise to itinerant and localized antiferromagnetism in quasi-one-dimensional organic conductors: the Bechgaard salts and their sulfur analogs. We will then focus on the problem of spin correlations and their impact on the pairing mechanism for organic superconductivity.

Fluctuations and Phase Separation in a Quasi-One-Dimensional System

“…Correlated systems exhibit a rich phase diagram with competing order parameters [1] and electronically driven phase transitions. Changes in doping, pressure, or chemical composition can give rise to quantum phase transitions (QPTs) [2] at T 0 K. Experimental examination of the competing phases has to cope with intense fluctuations at T > 0 and a tendency to phase separation [3,4].…”

Superconductor to spin-density-wave transition in quasi-one-dimensional metals with Ising anisotropy

“…A similar situation takes place in U < 0 Hubbard model on a square lattice [13] and in a certain Q1D system near charge density wave-singlet superconductivity transition [11]. In the latter paper the symmetry was investigated using non-Abelian bosonization technique [9] and found to be SU (2). On phenomenological level our model is an analog of SO(5) theory of high-T c superconductors proposed by S.-C. Zhang [14].…”

“…For models with the nearest neighbor interaction only and q = 0 the value of z coincides with the co-ordination number of a chain. In the above expression for E (2) a constant independent of ∆ c has been omitted. We see now that the condition for the mean field ground state to be a good approximation is…”

“…Two possibilities are discussed in the literature. One is BCS theory with the attraction mediated by either phonons or magnons [1,2]. The second approach developed by early workers in the field tries to accommodate the 'gology' picture of a one-dimensional conductor to the materials of interest [3].…”

Raman scattering study of phonon and spin modes in (TMTSF) 2 PF 6

“…According to these investigations the crossover temperature T ′ varies in the range 3 K-35 K. The theoretical estimations give even smaller magnitudes of T ′ . In the (TMTSF) 2 PF 6 model as weakly coupled Luttinger [38], and values of K ρ in the range 0.2-0.25 or 0.35 [39]. In contrast, the recent Hall effect and electrical conductivity measurements [6] in (TMTSF) 2 PF 6 confirm the Fermi-liquid description at T < ∼ 300K with the possible 1D Luttinger liquid picture well above room temperature.…”