Organic superconductors interactions

Attempts have also been made to design one-dimensional organic superconductors based on donor-acceptor interaction (Bechgaard Jerome, 1982). For this purpose it... 

A number of similarities [63] have been noted between properties of the organic superconductors such as (BEDT-TTF)2X, also known as (ET)2X, one of the ET salts, and those of the recently discovered cuprates, such as YBa2Cu307. Both have strong interactions in a plane with weak interactions out of the plane, giving a two-dimensional Fermi surface in both cases. The organics have portions of their Fermi surface that nest, and it appears now that this is also typical of the cuprates [64]. Both systems have a low density of carriers, with the result that screening is reduced, and therefore the electron-electron interactions are stronger than in an ordinary metal and electron-electron correlations are important in both cases. 

Fig. 12. View of the intermolecular S S interactions in (ET)2Br04. The top figure indicates the interstack S S contact distances less than the van der Waals sum of 3.60 A (298/125 K) d, = 3.581(2)/3.505(2), d2 = 3.499(2)/3.448(2), d3 = 3.583(2)/3.483(2), d4 = 3.628(2)/3.550(2), d5 = 3.466(2)/3.402(2), d6 = 3.497(2)/3.450(2), d7 = 3.516(2)/3.434(2), and d8 = 3.475(2)/3.427(2) A. The S S contact distances, d9-d16 (bottom), are, by contrast, all longer than 3.60 A even at 125 K. In addition the loose zig-zag molecular packing of ET molecules is such that they are not equally spaced, D, = 4.01/3.95 A and D2 = 3.69/3.60 A. As a result of the (apparently) weak intrastack and strong interstack interactions, (ET)2X molecular metals are structurally different from the previously discovered (TMTSF)2X based organic superconductors. Almost identical S S distances and interplanar spacings are observed in (ET)2Re04 at both 298 and 125 K. Only theoretical calculations will reveal the extent, if any, of chemical bonding associated with the various S S distances observed in (ET) X systems.

Prom the temperature dependence of the dHvA (or SdH) oscillations it is possible to extract the effective cyclotron mass (see Sect. 3.1). Comparisons of the mass obtained by these measurements with values from band-structure calculations, cyclotron resonance and specific-heat measurements are sometimes inconsistent. Whether strong electron-electron or electron-phonon interactions play the dominant role for this discrepancy is still under considerable debate and further studies have to deal with this question. Chapter 4 will review the present-day knowledge of the highly active field of the fermiology of organic superconductors . 

By using the donor TMTSF (tetramethyltetraselenafulvalene, 11b) and the newly developed technique of electrocrystallization, the groups of Bechgaard and Jerome found in 1990 the first organic superconductor, (TMTSF)2PF5, with Tj = 0.9 K at an applied pressure of 10 kbar [29]. Here the lateral two-dimensional Se-Se interactions and the applied pressure together defeat the Peierls transition. The first ambient-pressure superconductor, (TMTSF)2C104, followed quickly Fig. 4 shows its crystal structure. 

R586 P. Wzietek, S. Lefebvre, H. Mayaffre, S. Brown, C. Bourbonnais, D. Jerome, C. Meziere and P. Batail, Two-Dimensional Organic Superconductors Studied by NMR under Pressure , Hyperfine Interact., 2000,128,183... 

The nature of the pairing interaction remains an open question in organic superconductors. However, the existence of strongly developed antiferromagnetic fluctuations in (TMTSF)2X materials makes a non-phonon mediated pairing mechanism quite plausible. 

In Chapter 17, we introduce "electronic organic materials". The goal there is to describe new structures with novel electronic properties. These structures can be put to use as conducting or magnetic materials, and even organic superconductors. We will return to the interaction of light with matter in Chapter 17 when we describe photoresists and non-linear optics. 

Zhu J, Xu F, Schofer SJ, Mirkin CA. The first Raman spectrum of an organic monolayer on a high-temperature superconductor direct spectroscopic evidence for a chemical interaction between an amine and YBa2Cih07 < Journal of the American Chemical Society 1997, 119, 235-236. 

Another particular aspect of organic conductors is the extreme multiplicity of intra- and intermolecular vibrational modes to which the conduction electrons may couple. Then electron-phonon interactions are also of critical importance in the materials under the simple effect of such multiplicity. The electrical resistivity p is found to cover an extraordinary wide range of values, from exactly zero in superconductors below Tc, to more than 1010 fl cm in the most perfect insulators. 

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