Role of charge fluctuation in Q1D organic superconductor (TMTSF)2ClO4

TL;DR

This paper theoretically investigates how charge and spin fluctuations influence superconductivity in the quasi-one-dimensional organic superconductor (TMTSF)2ClO4, revealing novel order parameters and the coexistence of singlet and triplet states.

Contribution

It introduces a detailed multi-site Hubbard model analysis showing charge fluctuation-induced order parameters and the conditions for singlet and triplet superconductivity.

Findings

Charge fluctuations induce line-node order parameters.

Spin fluctuations reproduce anisotropic gap structures.

Triplet pairing emerges from combined charge and spin fluctuations.

Abstract

We have theoretically investigated the spin and charge fluctuations in the quasi-one dimensional organic superconductor (TMTSF)2ClO4. Using the extended multi-site Hubbard model, which contains four sites in a unit cell and the transfer energies obtained by the extended H\"uckel method, we calculate the linearized gap equation with the random phase approximation, to find novel order parameters of superconductivity due to several kinds of charge fluctuations induced by the anisotropic intersite repulsive interactions. For the singlet state, the order parameter with line nodes appears in the case of the strong charge fluctuation, while the order parameter with anisotropic gap suggested by Shimahara is reproduced in the spin fluctuation. The triplet state is also obtained for the wide parameter range of repulsive interactions due to a cooperation between charge and spin fluctuations.