# Microscopic theory of a superconducting gap in the quasi-one-dimensional organic conductor (TMTSF)$_2$ClO$_4$: Model derivation and two-particle self-consistent analysis

## TL;DR

This paper develops a microscopic model for the superconducting gap in the quasi-one-dimensional organic conductor (TMTSF)$_2$ClO$_4$, using first-principles calculations and a two-particle self-consistent analysis to estimate the critical temperature.

## Contribution

It derives an effective tight-binding model from first-principles and applies a TPSC analysis to investigate the pairing mechanism and gap symmetry in (TMTSF)$_2$ClO$_4$.

## Key findings

- The model predicts a d-wave-like gap with sign change between Fermi surfaces.
- Estimated critical temperature is approximately 1K, matching experimental data.
- Spin fluctuation-mediated pairing is supported as the superconducting mechanism.

## Abstract

We present a first-principles band calculation for the quasi-one-dimensional (Q1D) organic superconductor (TMTSF)$_2$ClO$_4$. An effective tight-binding model with the TMTSF molecule to be regarded as the site is derived from a calculation based on maximally localized Wannier orbitals. We apply a two-particle self-consistent (TPSC) analysis by using a four-site Hubbard model, which is composed of the tight-binding model and an on-site (intramolecular) repulsive interaction, which serves as a variable parameter. We assume that the pairing mechanism is mediated by the spin fluctuation, and the sign of the superconducting gap changes between the inner and outer Fermi surfaces, which correspond to a d-wave gap function in a simplified Q1D model. With the parameters we adopt, the critical temperature for superconductivity estimated by the TPSC approach is approximately 1K which is consistent with experiment.