Phase diagram of doped BaFe${}_2$As${}_2$ superconductor under broken $C_4$ symmetry

Abstract

We develop a minimal multiorbital tight-binding model with realistic hopping parameters. The model breaks the symmetry of the tetragonal point group by lowering it from $C_4$ to $D_{2d}$, which accurately describes the Fermi surface evolution of the electron-doped BaFe${}_{2-x}$Co${}_x$As${}_2$ and hole-doped Ba${}_{1-y}$K${}_y$Fe${}_2$As${}_2$ compounds. An investigation of the phase diagram with a mean-field $t$-$U$-$V$ Bogoliubov-de Gennes Hamiltonian results in agreement with the experimentally observed electron- and hole-doped phase diagram with only one set of $t$, $U$ and $V$ parameters. Additionally, the self-consistently calculated superconducting order parameter exhibits $s^{\pm }$-wave pairing symmetry with a small d-wave pairing admixture in the entire doping range, % The superconducting $s^{\pm }+d$-wave order parameter which is the subtle result of the weakly broken symmetry and competing interactions in the multiorbital mean-field Hamiltonian.

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