Effect of nonsymmorphic space groups on correlation functions in iron-based superconductors

The orbital basis is natural when one needs to calculate the effect of local interactions or to unravel the role of orbital physics in the response to external probes. In systems with nonsymmorphic point groups, such as the iron-based superconductors, we show that symmetries that emerge in observable response functions at certain wave vectors are absent from generalized susceptibilities calculated with tight-binding Hamiltonians in the orbital basis. Such symmetries are recovered only when the generalized susceptibilities are embeded back to the continuum using appropriate matrix elements between basis states. This is illustrated with the case of LiFeAs and is further clarified using a minimal tight-binding Hamiltonian with nonsymmorphic space group.