Theory of the beta-type Organic Superconductivity under Uniaxial Compression

TL;DR

This paper provides a theoretical analysis of how uniaxial compression affects the superconducting transition temperature in beta-type organic superconductors, highlighting the roles of electron correlation, spin frustration, and dimerization.

Contribution

It introduces a comprehensive theoretical framework combining Hubbard models and Eliashberg's equation to explain Tc behavior under uniaxial strain in different organic superconductors.

Findings

Dimer model accurately reproduces Tc in strongly dimerized beta-(BEDT-TTF)2I3.

Two-band model fits weakly dimerized beta-BDA-TTP salts.

Nonmonotonic Tc shifts are caused by competition between spin frustration and fluctuation effects.

Abstract

We study theoretically the shift of the superconducting transition temperature (Tc) under uniaxial compression in beta-type organic superconductors, beta-(BEDT-TTF)2I3 and beta-(BDA-TTP)2X[X=SbF6,AsF6], in order to clarify the electron correlation, the spin frustration and the effect of dimerization. The transfer integrals are calculated by the extended Huckel method assuming the uniaxial strain and the superconducting state mediated by the spin fluctuation is solved using Eliashberg's equation with the fluctuation-exchange approximation. The calculation is carried out on both the dimerized (one-band) and nondimerized (two-band) Hubbard models. We have found that (i) the behavior of Tc in beta-(BEDT-TTF)2I3 with a stronger dimerization is well reproduced by the dimer model, while that in weakly dimerized beta-BDA-TTP salts is rather well reproduced by the two-band model, and (ii) the competition between the spin frustration and the effect induced by the fluctuation is important in these materials, which causes nonmonotonic shift of Tc against uniaxial compression.