Mechanisms of Organic Superconductivity

Abstract

In applying the ideas of the preceding chapter to organic superconductors, it is necessary to keep in mind three essential experimental facts: (a) there is a crossover from spin-density wave order to superconductivity as the pressure is increased (b) there is no 2k_F charge-density wave and (c) the spin susceptibility is not activated. Using the general discussion of the previous chapter, it follows that U > 0 and V₁ (or an appropriate combination of V_n) is negative at high pressure. This conclusion is not restricted to the one-dimensional region but it does assume that the pairing involves electrons on the same stack. However, in the general context of organic conductors, it is not easy to imagine that V₁ can be as attractive as the experiments seem to require¹. There is ample evidence of quite strong repulsive interactions in organic conductors, and In the conventional BCS picture of superconductivity this has to be overcome by the retarded electron-phonon interaction, to produce pairing. For the latter, an electron or hole distorts the lattice in its immediate neighborhood, and a second electron or hole feels the distortion as an effective attractive coupling to the first. The Coulomb repulsion can be overcome because the distortion takes some time to decay, and is active after the first electron or hole has moved away.

Work supported by Division of Materials Sciences U.S. Department of Energy, under Contract No. DE-AC02-76CH00016.