Low-energy bound states at interfaces between superconducting and block antiferromagnetic regions in K_xFe_2-ySe₂

The high-T_c alkali doped iron selenide superconductors K _xFe_2-ySe₂ have been recently shown to be intrinsically phase separated into Fe vacancy ordered block antiferromagnetic regions and superconducting regions at low temperatures. In this work, we use a microscopic five orbital Hubbard model to obtain the electronic low-energy states near the interfaces between block antiferromagnets and superconductors. It is found that abundant low-energy in-gap bound states exist near such interfaces irrespective of whether the superconductor has d- or s-wave pairing symmetry. By contrast, it is shown how scattering from (110) boundaries can provide a natural means to distinguish between these two leading pairing instabilities of the K_xFe_2-ySe₂ materials.