Abstract
Superconductivity in the iron pnictides emerges from metallic parent compounds exhibiting intertwined stripe-type magnetic order and nematic order, with itinerant electrons suggested to be essential for both. Here we use x-ray and neutron scattering to show that a similar intertwined state is realized in semiconducting KFe0.8Ag1.2Te2 (K5Fe4Ag6Te10) without itinerant electrons. We find that Fe atoms in KFe0.8Ag1.2Te2 form isolated 2×2 blocks, separated by nonmagnetic Ag atoms. Long-range magnetic order sets in below TN≈35 K, with magnetic moments within the 2×2 Fe blocks ordering into the stripe-type configuration. A nematic order accompanies the magnetic transition, manifest as a structural distortion that breaks the fourfold rotational symmetry of the lattice. The nematic orders in KFe0.8Ag1.2Te2 and iron pnictide parent compounds are similar in magnitude and in how they relate to the magnetic order, indicating a common origin. Since KFe0.8Ag1.2Te2 is a semiconductor without itinerant electrons, this indicates that local-moment magnetic interactions are integral to its magnetic and nematic orders, and such interactions may play a key role in iron-based superconductivity.
