Bechgaard Salts Organic Superconductors

Bechgaard later used the even stronger electron acceptor molecule, perchlorate (CIO4), instead of PFg . He obtained a superconductor below Tc = 1.4 K at ambient pressure. All these organic conductors show magnetic ordering above the critical temperature up to several tens of kelvin, the transition temperature. 

FIG U RE 18.10 (See color insert) 8(TMTSF)+ and 4PFg as a part of two stacks. 

As in the case with (TMTSF)2PFg, the oxidizing molecule receives one electron per two molecules. 

Spin coupling occurs between two different pairs in some temperature regions. Apparently, this spin coupling provides the semiconductor gap in the non-conducting phases (for example, 65 cm in the case of TMTSF). 

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Exactly this approach led to the discovery of the first organic superconductors, the Bechgaard CT salts of tetramethyltetraselenafulvalene (TMTSF, 3) with various counteranions (TMTSF)2PF6 (under pressure) in 1980120 and... 

The neutral insulator TMTSF, which shows field-effect conduction with /Th — 0.2 cm s (Nam et al, 2003), when transformed into a Bechgaard salt also becomes superconducting, but at lower temperatures. In this case the perfect segregation of organic and inorganic molecular planes leads to confined electronic systems, which in the normal state are quasi ID. Organic superconductors based on the BEDT-TTF molecule represent the case of pure 2D electronic systems. 

At birth, the molecular metal was the one-dimensional metal. KCP and TTF-TCNQ are typical examples. The one-dimensional metal, however, is not a metal in the low temperature region due to the instability of the planar Fermi surface. Of course, this instability has provided rich physics [3], but is not favorable to the superconductivity. Therefore, chemists made efforts to increase the dimensionality of the electronic structure by the chemical modification with great success. The first organic superconducting system, the Bechgaard salt, is a quasi-one-dimensional system [4]. BEDT-TTF salts, the second-generation organic superconductors, have typical two-dimensional Fermi surfaces [5]. Three-dimensional Fermi surface has been found in the DCNQI-Cu salt [6]. 

TMTSFljX or Bechgaard Salts the First Organic Superconductors... 

Fig. 10.2 The crystal structure of the Bechgaard salt (TMTSF)2PF6, the first organic superconductor. The H atoms are - as usual -left off for clarity. The PFg anions are arranged between the stacks of the organic molecules. The perpendicular spacing within the stacks...

To be useful in ET, the DNA bases should be substituted with simpler orgauic moles of the type involved in the superconducting Bechgaard salts (Eigure 18.24). PFg molecules, which are easily reduced, should be used to create positive carriers in the same way as in the case of organic superconductors. 

Jensen was an efficient transmitter of the tradition of sulfur chemistry in Denmark, and several young scientists were inspired by him. For example, Bechgaard became a leading figure in the successful search for organic metals and superconductors ("Bechgaa salts") via his deep insight into sulto and selenium chemistry. 

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