Quasi-one-dimensional nanoscale modulation as sign of nematicity in iron pnictides and chalcogenides

Impurity scattering is found to lead to quasi-one-dimensional nanoscale modulation of the local density of states in iron pnictides and chalcogenides. This "quasiparticle interference" feature is remarkably similar across a wide variety of pnictide and chalcogenide phases, suggesting a common origin. We show that a unified understanding of the experiments can be obtained by simply invoking a fourfold symmetry breaking d(xz)-d(yz )orbital splitting, of a magnitude already suggested by the experiments. This can explain the one-dimensional characteristics in the local density of states observed in the orthorhombic nematic, tetragonal paramagnetic, as well as the spin-density-wave and superconducting states in these materials.