Enhancement of electron correlation due to the molecular dimerization in organic superconductorsβ−(BDA-TTP)2X(X=I3, 

Abstract

We perform a first principles band calculation for quasi-two-dimensional organic superconductors β-(BDA-TTP)2I3 and β-(BDA-TTP)2SbF6. The first principles band structures between the I3 and SbF6 salts are apparently different. We construct a tight-binding model for each material which accurately reproduces the first principles band structure. The obtained transfer energies give the differences such as (i) larger dimerization in the I3 salt than the SbF6 salt, and (ii) different signs and directions of the inter-stacking transfer energies. To decompose the origin of the difference into the dimerization and the inter-stacking transfer energies, we adopt a simplified model by eliminating the dimerization effect and extract the difference caused by the inter-stacking transfer energies. From the analysis using the simplified model, we find that the difference of the band structure comes mainly from the strength of dimerization. To compare the strength of the electron correlation having roots in the band structure, we calculate the physical properties originated from the effect of the electron correlation such as the spin susceptibility applying two particle self-consistent (TPSC) method. We find that the maximum value of the spin susceptibility of the I3 salt is larger than that of the SbF6 salt. Hypothetically decreasing the dimerization within the model of the I3 salt, the spin susceptibility takes almost the same value as that of the SbF6 salt for the same magnitude of the dimerization. We expect that the different ground state between the I3 and SbF6 salt mainly comes from the strength of the dimerization which is apparently masked in the band calculation along a particular k-path.

Two‐Particle Self‐Consistent Method for the Multi‐Orbital Hubbard Model

“…[149] and applied to study the semimetal to antiferromagnetic phase transition on a honeycomb lattice [149] and, the metal to superconducting transition in organic superconductors. [150][151][152] The first extension of TPSC to a multi-orbital formulation was introduced by Miyahara et al [153] where superconducting critical temperatures and gap symmetries with additional comparisons to RPA and FLEX were performed for high-Tc superconductors.…”

“…[149] and applied to study the semimetal to antiferromagnetic phase transition on a honeycomb lattice [ 149 ] and, the metal to superconducting transition in organic superconductors. [ 150–152 ]…”

Microscopic theory of the superconducting gap in the quasi-one-dimensional organic conductor (TMTSF)2ClO4 : Model derivation and two-particle self-consistent analysis

“…6. We do not consider this suppression caused by the Mermin-Wagner theorem, because according to this theorem, the eigenvalue of U sp χ 0 asymptotically approaches unity if the SDW state is suppressed [101]. The eigenvalue of U sp χ 0 saturates below unity at lower temperature, as shown in Fig.…”

The two-particle self-consistent approach and its application to real materials

“…The presentation of this section is based on [154,161,164]. Going from single-band TPSC to a multi-site formulation is basically a change in the notation without additional new terms [152,239,240]. Nevertheless, we present the important equations and steps with all details since we presented only the basic ideas in the single-band case in sec.…”

“…The multisite version of TPSC was applied to the Hubbard model on a honeycomb lattice where antiferromagnetic instabilities were studied [152]. Further investigations dealt not only with superconductivity in organic superconductors [239,241,242] and Cuprate superconductors [240,243,244] but also with correlation effects in layered transition metal dichalcogenides [245]. The approach was also used to define a measure for the strength of k-dependence of the self-energy [246].…”