Symmetry and Gap Classification of the non-symmorphic SrPtAs

The hexagonal superconductor SrPtAs exhibits time-reversal-symmetry breaking below $T_c$, hinting at an unconventional pairing state. Therefore, the symmetry of the underlying crystal is important for the classification of possible gap structures and their mixing. Here, we use the generating point group D$_{6h}$ of SrPtAs for a comprehensive classification of the gap functions and to construct a tight-binding model. Our work clarifies questions of symmetry and topology in this non-symmorphic material and allows for better comparison with other hexagonal systems.