Repulsive interaction helps superconductivity in fullerides

TL;DR

This paper investigates how purely repulsive interactions influence superconductivity in fullerides, revealing that certain symmetries are favored depending on lattice structure and that electron-phonon interactions can stabilize s-wave pairing.

Contribution

It introduces a weak-coupling model for repulsive interactions in fullerides, analyzing symmetry preferences and the impact of electron-phonon coupling on superconducting states.

Findings

The $T_g$ symmetry is most stable in bcc lattices with repulsive interactions.

Various symmetries have comparable coupling strengths in fcc lattices.

Electron-phonon interactions can stabilize the $A_g$ s-wave pairing.

Abstract

A repulsive interaction model of superconductivity (SC) is studied for tight-binding models with three-fold degenerate molecular orbitals. Taking a weak-coupling approach, we derive dimensionless coupling constants for various symmetries of SC pairs. In addition to anisotropic SC pairs, the s-wave pairing ($A_g$) can also be formed. With the purely repulsive interaction, however, the $A_g$ pair is not the most stable in both bcc and fcc lattices. The most stable SC pair for the bcc lattice has the $T_g$ symmetry, which is favored by a strongly nesting Fermi surface. In the fcc lattice, various SC symmetries have comparable coupling strengths. With the electron-phonon interaction combined, it is likely that the $A_g$ pair becomes the most stable.