Superconducting pairing from repulsive interactions of fermions in a flat band system*

Many-body quantum systems of fermions with flat bands at the Fermi level are intensely studied for their potential to boost superconductivity by enhancement of the density of states. We use quasiexact numerical methods to show that repulsive interactions between spinless fermions in a model one-dimensional flat band system, the Creutz ladder, lead to a finite pairing energy that increases with repulsion. Pure repulsion however leaves charge-order as the dominant quasi-order over the superconductivity. Adding an additional attractive component to the interaction shifts the balance fully in favor of superconductivity. In this regime we find that the interactions of two flat bands further yields a remarkable enhancement to superconductivity far above and outside the known paradigms for one-dimensional fermions.