Interaction created effective flat bands in conducting polymers

TL;DR

This paper demonstrates how interaction effects can create effective flat bands in conducting polymers with complex unit cells, leading to non-saturated ferromagnetism distinct from traditional flat-band ferromagnetism.

Contribution

It provides an exact demonstration of interaction-induced flat bands in conducting polymers with inhomogeneous Coulomb interactions, expanding understanding beyond known flat-band systems.

Findings

Interaction creates effective flat bands in conducting polymers.

Emergence of non-saturated ferromagnetic states due to kinetic energy quench.

Flat bands appear without bare flat bands, requiring inhomogeneous Coulomb interactions.

Abstract

For a general class of conducting polymers with arbitrary large unit cell and different on-site Coulomb repulsion values on different type of sites, I demonstrate in exact terms the emergence possibility of an upper, interaction created "effective" flat band. This last appears as a consequence of a kinetic energy quench accompanied by a strong interaction energy decrease, and leads to a non-saturated ferromagnetic state. This ordered state clearly differs from the known flat-band ferromagnetism. This is because it emerges in a system without bare flat bands, requires inhomogeneous on-site Coulomb repulsions values, and possesses non-zero lower interaction limits at the emergence of the ordered phase.