Electron-phonon Coupling In Low-dimensional Organic Superconductors

The relative importance of the coupling of electrons with intra- and inter-molecular phonons in setting up the organic superconductivity is addressed. We base our considerations on a firmly established set of electron molecular vibration coupling constants for the TMTTF molecule. By the use of three different models of the BCS, strong coupling and non adiabatic type we find that, in order to attain critical temperatures (T(c)) in the typical range of 1 to 10 K, large values for the electron inter-molecular phonon coupling constants are needed. We also report a theoretical analysis of the effects of isotopic substitution of the carbon atoms in a TTF based molecule. Through a simple model of two coupled oscillators and by the use of the experimental data available for TMTTF, we estimate isotopic T(c) shifts which may be useful for qualitative comparison with experimental data.