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

TL;DR

This study develops a minimal multiorbital model for doped BaFe$_2$As$_2$ superconductors, capturing the Fermi surface evolution and phase diagram under broken $C_4$ symmetry, revealing an $s^ ext{±}$-wave pairing with a small d-wave component.

Contribution

It introduces a realistic multiorbital tight-binding model that incorporates symmetry breaking and accurately reproduces experimental phase diagrams with a unified parameter set.

Findings

The model reproduces the Fermi surface evolution in doped BaFe$_2$As$_2$ compounds.

The phase diagram aligns with experimental observations using a single parameter set.

Superconducting order exhibits $s^ ext{±}$-wave symmetry with a minor d-wave admixture.

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.