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

TL;DR

This paper investigates how nonsymmorphic space group symmetries influence correlation functions in iron-based superconductors, revealing that certain symmetries are only apparent when susceptibilities are properly embedded into the continuum.

Contribution

It demonstrates that symmetries in response functions are absent in orbital basis calculations but can be recovered through continuum embedding, clarifying the role of nonsymmorphic symmetries.

Findings

Symmetries in response functions are absent in orbital basis susceptibilities.

Embedding susceptibilities into the continuum restores these symmetries.

Application to LiFeAs illustrates the importance of proper embedding.

Abstract

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 non-symmorphic space group.