Superlight pairs in face-centred-cubic extended Hubbard models with strong Coulomb repulsion

TL;DR

This paper shows that in FCC lattice extended Hubbard models with strong Coulomb repulsion, tightly bound, lightweight pairs can form and potentially Bose condense at high temperatures, explaining high-Tc fulleride superconductivity.

Contribution

It reveals that FCC structures uniquely support strongly bound, light pairs in extended Hubbard models, differing from other cubic lattices.

Findings

FCC lattices support strongly bound, light pairs.

Pairs can Bose condense at high temperatures.

Results applicable to fulleride superconductors.

Abstract

The majority of fulleride superconductors with unusually high transition-temperature to kinetic-energy ratios have a face-centred-cubic (FCC) structure. We demonstrate that, within extended Hubbard models with strong Coulomb repulsion, paired fermions in FCC lattices have qualitatively different properties than pairs in other three-dimensional cubic lattices. Our results show that strongly bound, light, and small pairs can be generated in FCC lattices across a wide range of the parameter space. We estimate that such pairs can Bose condense at high temperatures even if the lattice constant is large (as in the fullerides).