Perturbation Theory on the Transition Temperature and Electronic Properties of Organic Superconductor

Abstract

We study the superconducting transition temperature and the electronic properties of the metallic phase of $\kappa$-type (BEDT-TTF)${}_2$X which shows unconventional properties in experiments, on the basis of the third order perturbation theory for a simple effective Hubbard model of a nearly triangular lattice. Appropriate transition temperatures and $d_{x^2-y^2}$ symmetry of the gap function are obtained in good agreement with experimental results. We also calculate the transition temperature by the fluctuation-exchange approximation(FLEX) in order to compare the two approaches; FLEX gives higher transition temperatures rather than the perturbation approach. However, it is also found that the vertex corrections, which are ignored in FLEX, have a crucial effect on $T_{\mathrm{c}}$ for strongly frustrated systems. The density of states and the normal self-energy calculated in this perturbation scheme show the nature of the conventional Fermi liquid near the Mott-insulator. Thus, our perturbation approach is applicable to the conventional metallic phase of this compound, while it cannot explain the (pseudo-)spin gap phenomenon which signals the non-Fermi liquid.

References in corpus (5)

• Similarities between organic and cuprate superconductors
• Pairing due to Spin Fluctuations in Layered Organic Superconductors
• Phase Diagram of Superconductivity on the Anisotropic Triangular Lattice Hubbard Model
• Electronic structure of underdoped cuprates
• Nearly Antiferromagnetic Fermi Liquids: A Progress Report

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