Interplay of mass imbalance and frustration in correlated band insulators

TL;DR

This paper explores how mass imbalance and frustration in a variant of the Hubbard model induce exotic magnetic metallic phases and superconductivity, revealing new phases and behaviors in correlated band insulators.

Contribution

It introduces a comprehensive phase diagram for the ionic Hubbard model with mass imbalance, highlighting the emergence of novel magnetic metallic phases and superconducting states.

Findings

Emergence of spin imbalanced ferromagnetic metal

Observation of ferrimagnetic and antiferromagnetic half metals

Detection of singlet superconductivity in strong coupling limit

Abstract

We report the emergence or broadening of exotic magnetic metallic phases upon explicit breaking of $SU(2)$ symmetry by introduction of mass imbalance in a variant of Hubbard model, known as the ionic Hubbard model in the presence of frustration at half-filling on a square lattice. The ionic Hubbard model has in addition to hopping($\sim t$) and onsite coulomb repulsion ($\sim U$), a staggered ionic potential ($\sim \Delta$) which breaks translational symmetry of the underlying lattice. In the low to intermediate ranges of $U$ and $\Delta$, we use unrestricted Hartree-Fock theory to construct the phase diagram in the $U-\Delta$ plane for a fixed mass imbalance($\sim\eta$). Where as in the limit where both $U,\Delta$ are comparable and much larger than the first $(\sim t_{\sigma})$ and second $(\sim t_{\sigma}')$ neighbor hopping amplitudes , we employ the technique of generalized Gutzwiller approximation and subsequently use renormalized mean field theory to construct the phase diagram for varying values of hopping asymmetry. In both cases, starting from a correlated band insulator with weak antiferromagnetic spin density wave order, if we tune $U/\Delta$, we observe the opening of novel magnetically ordered metallic phases such as spin imbalanced ferromagnetic metal, ferrimagnetic metal and antiferromagnetic half metal. We also study singlet superconductivity in the d-wave and extended s-wave channels in the strong coupling limit of this model in the presence of mass imbalance.