A series of experiments revealed that novel bipartite magnetic and superconducting (SC) phases widely exist in the phase diagrams of iron pnictides and chalcogenides. Nevertheless, the origin of the two-dome magnetic and SC phases in iron-based compounds remains unclear. Here we theoretically investigated the electronic structures, magnetic, and SC properties of three representative iron-based systems, i.e., ${\mathrm{LaFeAsO}}_{1-x}{\mathrm{H}}_x, {\mathrm{LaFeAs}}_{1-x}{\mathrm{P}}_x\mathrm{O}$, and ${\mathrm{KFe}}_2{\mathrm{As}}_2$. We propose a unified quasidegenerate orbital mechanism for the emergence of the two-dome parent magnetic/structural phase and the subsequent two-dome SC phase. It is found that the degenerate in-plane anisotropic $d_{xz/yz}$ orbitals dominate the first magnetic/structural and SC phases, while in-plane isotropic orbitals $d_{xy}$ or $d_{3z^2-r^2}$ with quasidegeneracy originating from quasisymmetry drive the emergence of the second magnetic/SC dome phase. Moreover, a matching rule of spin and orbital modes for SC pairing state is proposed in multiorbital iron-based systems. These results imply an orbital-driven mechanism as well as an orbital-selective scenario and shed light on the understanding of the multidome magnetic and SC phases in multiorbital systems.

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• Electronic structure
• Superconductivity
• Iron-based superconductors
• Density functional calculations
• Tight-binding model
• Wannier function methods