One Dimensional Fabre- & Bechgaard-Salts
Fabre-Salts are composed of tetramethyltetrathiafulvalene (TMTTF) and Bechgaard-salts of tetramethyltetraselenafulvalene (TMTSF). These two organic molecules are similar except for the sulfur-atoms of TMTTF being replaced by selenium-atoms in TMTSF. The molecules are stacked in columns (with a tendency to dimerization) which are separated by anions. Typical anions are for example octahedral PF6, AsF6 or tetrahedral ClO4 or ReO4.
Both material classes are quasi one-dimensional at room-temperature only conducting along the molecule stacks and share a very rich phase diagram containing antiferromagnetic ordering, charge order, spin-density wave state, dimensional crossover and of course superconductivity.
Only one Bechgaard-Salt was found to be superconducting at ambient pressure which is (TMTTF)2ClO4 with a transition temperature of TC = 1.4 K. Several other salts become superconducting only under external pressure. The external pressure one would have to apply to drive most Fabre-salts to superconductivity is so high, that under lab conditions superconductivity was observed only in one compound. A selection of the transition temperature and corresponding external pressure of several one-dimensional organic superconductors is shown in the table below.
| Material | TC (K) | pext (kbar) |
|---|---|---|
| (TMTSF)2SbF6 | 0.36 | 10.5 |
| (TMTSF)2PF4 | 1.1 | 6.5 |
| (TMTSF)2AsF6 | 1.1 | 9.5 |
| (TMTSF)2ReO4 | 1.2 | 9.5 |
| (TMTSF)2TaF6 | 1.35 | 11 |
| (TMTTF)2Br | 0.8 | 26 |
Read more about this topic: Organic Superconductor
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