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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.
Magnetic measurements on optimally doped single crystals of BaFe$_2$(As$_{1-x}$P$_{x}$)$_2$ ($xapprox0.35$) with magnetic fields applied along different crystallographic axes were performed under pressure, enabling the pressure evolution of coherence
Systematic measurements of the resistivity, heat capacity, susceptibility and Hall coefficient are presented for single crystal samples of the electron-doped superconductor Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$. These data delineate an $x-T$ phase diagram i
We investigated the complex conductivity spectrum of a Co-doped BaFe$_2$As$_2$ epitaxial thin film in the THz region. In the normal state, the complex conductivity shows a Drude-type frequency dependence, while in the superconducting state, the frequ
Inelastic neutron scattering measurements on Ba(Fe$_{0.963}$Ni$_{0.037}$)$_2$As$_2$ manifest a neutron spin resonance in the superconducting state with anisotropic dispersion within the Fe layer. Whereas the resonance is sharply peaked at Q$_{AFM}$ a
In many classes of unconventional superconductors, the question of whether the superconductivity is enhanced by the quantum-critical fluctuations on the verge of an ordered phase remains elusive. One of the most direct ways of addressing this issue i