Organic Superconductors: A Survey of Low Dimensional Phenomena

An experimental investigation of the electronic properties of the conducting cation radical salts (TMTSF)₂X, has shown how the development of superconductivity at low temperature is affected by the low dimensional character of the band structure. Electron Schottky tunnel spectroscopy has given evidence that the critical temperature is not an intrinsic property of the intrachain superconducting pairing. The pairing energy in (TMTSF)₂PF₆ (P=11 Kbar) derived from the pseudo-gap in the quasi particle density of states amounts to ≈40 K i.e about 40 times the critical temperature. Consequently, properties such as conductivity, thermal conductivity, thermopower, etc… of these Quasi-One-Dimensional Superconductors are to a large extent dominated by the onset of 1-D fluctuating superconducting pairing below 30 K or so. Moreover, the stabilization of these fluctuations into a 3-D ordered superconducting state at higher temperature, namely 12 K for (TMTSF)₂PF₆, (P=11 Kbar) seems feasible via chemically induced chain bridging. The large pairing energy as well as the presence of a spin density waves state in the (T.P) phase diagram of these organic superconductors suggest the importance of the Coulomb interactions in the mechanism of Cooper pair formation.