Electronic Mechanism for the Coexistence of Ferroelectricity and Ferromagnetism

TL;DR

This paper demonstrates that in a two-band Hubbard model with opposite parity bands at quarter filling, the ground state can simultaneously exhibit ferromagnetism and ferroelectricity, leading to a singular magnetoelectric effect.

Contribution

It provides a theoretical proof of coexistence of ferroelectricity and ferromagnetism in a specific strongly correlated electron model.

Findings

Ground state is both ferromagnetic and ferroelectric under certain conditions.

Coexistence results in a singular magnetoelectric effect.

Valid in the strong coupling limit with infinite intra-orbital Coulomb interactions.

Abstract

We study the strong coupling limit of a two-band Hubbard Hamiltonian that also includes an inter-orbital on-site repulsive interaction $U_{ab}$. When the two bands have opposite parity and are quarter filled, we prove that the ground state is simultaneously ferromagnetic and ferroelectric for infinite intra-orbital Coulomb interactions $U_{aa}$ and $U_{bb}$. We also show that this coexistence leads to a singular magnetoelectric effect.