Pairing due to Spin Fluctuations in Layered Organic Superconductors

TL;DR

This paper demonstrates that short-range antiferromagnetic spin fluctuations can induce superconductivity with a transition temperature around 10 K and gap nodes in layered organic superconductors, using a two-band model and fluctuation exchange approximation.

Contribution

It introduces a self-consistent two-band model showing how spin fluctuations cause pairing in ppa-type organic superconductors, highlighting inter-band coupling effects.

Findings

Superconductivity with T_c a9 10 K is explained by spin fluctuations.

Gap nodes are present on the Fermi surface due to the pairing mechanism.

Inter-band coupling plays a dominant role in the pairing interaction.

Abstract

I show that for a \kappa-type organic (BEDT-TTF)_2-X molecular crystal, a superconducting state with T_c ~ 10 K and gap nodes on the Fermi surface can be caused by short-ranged antiferromagnetic spin fluctuations. Using a two-band description for the anti-bonding orbitals on a BEDT-TTF dimer of the \kappa-type salt, and an intermediate local Coulomb repulsion between two holes on one dimer, the magnetic interaction and the superconducting gap-function are determined self consistently within the fluctuation exchange approximation. The pairing interaction is predominantly caused by inter-band coupling and additionally affected by spin excitations of the quasi one-dimensional band.