Interplay of mass imbalance and frustration in correlated band insulators

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 ($\sim Δ$) which breaks translational symmetry of the underlying lattice. In the low to intermediate ranges of $U$ and $Δ$, we use unrestricted Hartree-Fock theory to construct the phase diagram in the $U-Δ$ plane for a fixed mass imbalance($\simη$). Where as in the limit where both $U,Δ$ are comparable and much larger than the first $(\sim t_σ)$ and second $(\sim t_σ')$ 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 $U/Δ$, 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.