The Origin of Pairing Interaction in Organic Superconductors

Abstract

A problem of great importance in the study of organic conductors is the characterization of the microscopic conditions giving rise to superconductivity in these compounds. Looking at the phase diagram of the Bechgaard salts series (TMTSF)₂X (X= PF₆, AsF₆, C10₄, …),^1,2 this problem seems to be intrinsically linked to the puzzling proximity between superconducting and antiferromagnetic long range order. The existence of antiferromagnetism and the absence of a Peierls transition is known to be a strong indication in favor of dominant repulsive interactions among electrons. This has been used to challenge the traditional role played by phonons in the superconductive pairing interaction and to infer a participation of electron spin correlations in the pairing mechanism.^3–5In this paper we will be mainly concerned with clarifying the microscopic origin of this proximity, especially to specify the mechanism by which antiferromagnetism is itself stabilyzed and to what extend it can exert an influence on the metallic state where the pairing interaction is formed. More specifically, we overview the implications of recent calculations for the quasi-1D electron gas model. The existence and the importance of the interchain antiferromagnetic exchange coupling for the stabilyzation of antiferromagnetism are demonstrated.⁴ We also discuss how this mechanism can lead to high-temperature superconducting correlations.