First-Order Phase Transition Boundary between Superconducting and SDW Phases in the Bechgaard Salts

Abstract

Near the SDW-normal phase boundary obtained previously as a function of the transverse transfer energy t ' on a quasi 1D Hubbard model, the purely superconducting state is found to extend into the SDW region, once it appears in the normal region. The titled boundary is calculated on the basis of the above-mentioned model added with an anisotropic BCS-type interaction. The obtained curve well reproduces the observed T P phase diagram, if we take \(t{'}{\cong }300\) k B and d t '/d P ∼0.6 k B /kbar. A new RPA expression of the anisotropic plasma frequency for the present model provides the value of t ' in remarkable agreement with the above estimate. Examination of the coupled equations for the two kinds of order parameters leads to conclude no microscopic coexistence of them. Quasi 1D conductors are argued to be favorable to realize the triplet superconductivity.