This review attempts to present the most salient developments of research on organic conductors and superconductors during the past 10 years. A theoretical introduction treats instabilities of quasi-one-dimensional electron systems and associated precursor effects which are relevant to the experimental results on organic conductors. We then describe the characterization of quasi-one-dimensional organic conductors by their transport, optical and magnetic properties. Finally, two sections are devoted to the experimental investigation of the low temperature instabilities: lattice instability in TTF-TCNQ and related compounds, superconducting or antiferromagnetic instabilities in the (TMTSF) 2 X series. The importance of one-dimensional fluctuations is emphasized in both lattice and superconducting instabilities.

Organic conductors and superconductors

Recent progress on conducting organic charge-transfer salts

Superconductivity, that is, the possibility for electrons to flow through a conductor without any energy loss, has been the fuel for a very large number of industrial applications of physics in the twentieth century. Just to mention some of them which are important in current life, we have the power loss energy transfer, the production of very strong magnetic fields for medical imaging or for plasma confinement (the fusion problem) voltage standards, particle accelerators, and magnetic flux sensors.

Organic conductors: from charge density wave TTF-TCNQ to superconducting (TMTSF)2PF6.

The upper temperature for superconductivity in organic conductors has increased from 1 kelvin in 1980, when the phenomenon was discovered in the quasi-one-dimensional cation radical salt tetramethyltetraselenafulvalene phosphorus heptafluoride to 12 kelvin in a new series of organic salts that show nearly two-dimensional electronic properties. These superconductors are attracting interest because of the wide range of new phenomena that they exhibit, including the competition between various ground states, the influence of a magnetic field on a quasi-one-dimensional conductor, the quantization of the Hall effect in a three-dimensional material, the giant magnetoresistance effects related to the two-dimensional nature of the Fermi surface of some materials, and the coherent voltage oscillation of a spin-modulated ground state. Furthermore, there is reason to believe that organic conductors with high superconducting transition temperatures could be produced in the near future. The recent finding of superconductivity in "fullerene" doped with alkali metals supports this optimism.

https://science.sciencemag.org/content/sci/252/5012/1509.full.pdf

The physics of organic superconductors.

Organic−inorganic hybrid films present special challenges and opportunities with respect to potential applications, as well as for the observation of interesting physical phenomena. Although the often disparate characteristics (e.g., solubility and thermal stability) of the two components provide a potential barrier toward forming workable and convenient film deposition strategies, recent results have demonstrated that not only is it possible to develop suitable techniques for these materials but relatively simple processes are often sufficient to yield high quality films. In the current review, some of these recent results on organic−inorganic hybrid films are discussed, with selected examples chosen from among the deposition of sol−gel materials, self-assembled hybrids, Langmuir−Blodgett films, and artificially layered materials. In addition to discussing film-deposition techniques, an effort will also be made, where appropriate, to indicate how the resulting films might be useful for applications such ...

Thin-Film Deposition of Organic−Inorganic Hybrid Materials

Evidence for superconductivity in (BEDT-TTF) 4 (ReO 4) 2 [where BEDT-TTF is bis(eth-ylenedithiolo)tetrathiafulvalenel near 2 K for pressures above 4 kbar is reported. This is the first unambiguous observation of superconductivity in a sulphur-donor organic system. At higher pressures the transition temperature decreases rapidly, dT c,/dP~- 0.3 K/kbar. At low pressures this material exhibits a first-order metal-insulator transition, postulated to result from a change in the arrangement of the anions which are ordered at room temperature.

Superconductivity in a new family of organic conductors

A major feature of the ET molecule is its ability to form many different phases and structures with the same or different anions Whilst this considerably complicates the growth and characterisation of these materials this does allow a systematic study of compounds differing only in charge state or crystal structure, but otherwise containing the same donor and acceptor species We show that ET forms at least four different phases with the ReO4 −anion, allowing such a systematic study We show that one of these, γ-ET3(ReO4)2, is the only currently known example of an ET charge transfer salt in which the anions are not ordered at room temperature We find the anions become ordered at a lower temperature We show that anions smaller than some certain value stabilise a single phase containing 3 ET molecules for every two anions and that larger anions form different sets of crystal structures

The Many Faces of ET

The structure, conductivity, and thermopower of HMTTF-TCNQ

Various synthetic procedures for preparing BEDT-TTF are critically examined. Starting from readily available thiapendione, BEDT-TTF can be made in a high yield, simple, two-step synthesis. Electrochemical crystal growth of charge transfer complexes of BEDT-TTF typically involves the formation of multiple phases and stoichiometries. In the case of perrhenate (ReO- 4) at least five different complexes have been identified. Controlled preparation of the superconducting phase (BEDT-TTF2ReO4) remains an elusive goal.

R. R. Schumaker

Papers

Superconductivity in a new family of organic conductors

The Many Faces of ET

The structure, conductivity, and thermopower of HMTTF-TCNQ

Synthesis of Biethylenedithiolylene-Tetrathiafulvalene Donors (BEDT-TTF) and Electrochemical Preparation of their Charge Transfer Complexes

Electron-electron interactions in the fulvalene family of organic metals