Mechanisms of Organic Superconductivity
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 2kF 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 Vn) 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.
KeywordsHubbard Model Spin Fluctuation Previous Chapter Spin Susceptibility Organic Conductor
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- 2.I thank J. Voigt and S. Barišić for discussion of this point.Google Scholar
- 4.The experiment4 did not actually extend into the superconducting phase and, in principle another structural transition could intervene.Google Scholar
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