TMTSF superconductor

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... 

As will be discussed later (Section 1.5), molecules containing no metallic elements are able to combine and form materials exhibiting metallic character, e.g., HMTSF-TCNQ, TTF-TCNQ, etc., or even lose any electrical resistance below a given temperature and thus become superconductors, e.g., (TMTSF)2C104. Metal-free molecules can also, in the solid state, show magnetic order, such as / -NPNN and /7-NC-C6F4-CNSSN, where in the absence of -electrons the magnetic properties are related to unpaired -electrons. 

TMTSF)2C104 exhibits Tc - 1 -4 K at P = 0 GPa, hence becoming the hrst organic superconductor at ambient pressure (Bechgaard etal, 1981). The tetrahedral... 

CIO4 tetrahedra have the same orientation in a given ac-plane while the orientation alternates in the fc-direction. Since the period along a is preserved, no gap opening is expected at T o, as experimentally verihed (Gubser et al, 1982). This is the reason why (TMTSF)2C104 becomes a superconductor in spite of the anion ordering transition. 

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. 

Scheme 15 Component molecules for molecular superconductors except TMTSF, TMTTF, FT and BO systems. Numbers in bracket are the total members of each superconductor and the highest (in K)...

Takahashi T, Kobayashi Y, Nakamura T, Kanoda K, Hilti B, Zamhounis IS (1994) Symmetry of the order parameter in organic superconductors (MDT-TTF)2Aul2 vs. (TMTSF)2C104. Physica C 235-240 2461-2462... 

For example, recently some selenium derivatives of TTF (i.e., TMTSF) were found to become superconductors around 1... 

Research in the area of new synthetic metal (synmetal) superconductors continues to be stimulated by rapid developments in the chemistry and physics of these materials.1 Synmetals are unique in that they have metallic properties even though they contain no metals. However, this field remains very much materials limited because, as yet, it is not possible to predict which new materials will exhibit metallic properties. This situation is improving because structure-property correlations have been developed recently that may be used to predict likely candidates for superconductivity in the 4,4 j5,5 -tetramethyl-2,2 -bi-l-3-diselenolylidene, often called the tetra-methyltetraselenafulvalene (TMTSF) class of materials.2... 

Figure 8 Slipped and staggered relationship of TMTSF molecules in superconductors the relative positions are approximate...

So far all TMTSF and almost all ET-type superconductors have mixed valence and p=. The TMTSF salts and some ET salts are quasi-ID, but with enough warping of the Fermi surface to make them pseudo-2D and to defeat the Peierls transition. The k-phase (BEDT-TTF) salts are really 2-D systems this phase, shown in Fig. 12.7, has isolated dimers connected by dispersion interactions to form, roughly, two-dimensional sheets. Figure 12.8 shows the superconductivity of the salt k-(BEDT-TTF)2Cu(NCS)2 at 10.4 K [34]. 

The second milestone was the discovery of the first organic superconductor, (TMTSF)2PF6, by Jerome et al. [33] in 1980 with a transition temperature of 0.9 K at a pressure of 12 kbar. This opened the door to the discovery of other charge-transfer superconductors that were found to superconduct at ambient pressure and with higher transition temperatures. Today more than 30 such superconductors have been synthesized and characterized, and the highest transition temperature among this class is now in excess of 12 K. 

TMTSF)2C104 [TMTSF is tetramethyltetraselenafulvalene], an ambient-pressure one-dimensional superconductor of the Bechgaard salt family... 

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