Nonsymmorphic symmetry and field-driven odd-parity pairing in CeRh2As2

Recently, evidence has emerged for a field-induced even- to odd-parity superconducting phase transition in CeRh2As2 [S. Khim et al., Science 373, 1012 (2021)]. Here we argue that the P4/nmm nonsymmorphic crystal structure of CeRh2As2 plays a key role in enabling this transition by ensuring large spin-orbit interactions near the Brillouin zone boundaries, which naturally leads to the required near-degeneracy of the even- and odd-parity channels. We further comment on the relevance of our theory to FeSe, which crystallizes in the same structure.