Electronic mechanism for the coexistence of ferroelectricity and ferromagnetism

Abstract

We study the strong-coupling limit of a two-band Hubbard Hamiltonian that includes an interorbital 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 intraorbital Coulomb interactions ${U}_{aa},{U}_{bb}\ensuremath{\gg}{U}_{ab}$. We also show that this coexistence leads to an enormous magnetoelectric effect.