Can Excitonic Mechanism Contribute Significantly to Superconducting Pairing in Quasi 1-D Systems?

Abstract: We have revisited Cooper's one pair problem of calculating the binding energy for two electrons, experiencing an attractive interaction near the Fermi surface, in case of quasi one dimensional lattice system. Though it is a generalized formalism, we have chosen two materials viz., (TMTSF)2ClO4 and (TMTSF)2AsF6 as examples. Some of their electronic and optical features are used for calculations and validity this formalism is checked too for these materials. It is generally believed that spin density fluctuation mechanism is very strong candidate for the occurrence of superconductivity in these quasi one dimensional materials. We have attempted to invoke another type of electronic mechanism viz., charge transfer Exciton mechanism to explore if some substantial contribution for attractive coupling can be generated. This mechanism may be plausible in these types of organic materials where ionicity and co-valency co-exist. Making use of the experimental results for optical absorption spectra corresponding to above materials, we extracted the relevant parameters for incorporating in the binding energy calculation. Our calculation shows that Fermionic pair formation is possible for all the three cases viz., (1) less than half filled, (2) half filled and (3) more than half filled.