Correlation driven metallic and half-metallic phases in a band insulator

Abstract

We demonstrate a mechanism for realizing ferrimagnetic metal, antiferromagnetic half-metal, and paramagnetic metal phases by tuning the onsite Coulomb repulsion $U$ in a band insulator. In a simple model of a correlated band insulator, namely the ionic Hubbard model at half-filling, and in the presence of a second neighbor hopping, we show that as $U$ is increased, first he insulating band gap is suppressed to zero at a critical ${U}_{1}$ and remains zero within the paramagnetic metallic phase. Interestingly, at a larger ${U}_{c}$, ferrimagnetic order turns on, leading to a ferrimagnetic metallic phase for ${U}_{c}<U<{U}_{2}$. For $U>{U}_{2}$, the system exhibits an antiferromagnetic half-metallic phase, followed finally by a transition into an antiferromagnetic Mott insulator. Our results, based on dynamical mean-field theory, suggest alternate routes for achieving magnetically ordered metallic and half-metallic phases which have potential applications in spintronics.