Origin of electronic dimers in the spin-density wave phase of Fe-based superconductors

We investigate emergent impurity-induced states arising from pointlike scatterers in the spin-density wave phase of iron-based superconductors within a microscopic five-band model. Independent of the details of the band structure and disorder potential, it is shown how stable magnetic (π,π) unidirectional nematogens are formed locally by the impurities. Interestingly, these nematogens exhibit a dimer structure in the electronic density, are directed along the antiferromagnetic a axis, and have typical lengths of ∼10 lattice constants, in excellent agreement with recent scanning tunneling experiments. These electronic dimers provide a natural explanation of the dopant-induced transport anisotropy found, e.g., in the 122 iron pnictides.