Abstract: Improper phases are characterized by a secondary order parameter setting in as a direct consequence of a primary order. In this talk, we highlight an overlooked mechanism that couples order parameter bilinears to odd-parity order parameters such that the latter emerge as improper orders. To this end, we explore a novel perspective on nonsymmorphic symmetries based on extended symmetry groups in real space. We demonstrate how nonsymmorphic symmetries can generate rather nonintuitive couplings between order parameters. We are inspired by the phenomenology of the recently discovered superconductor CeRh2As2, but our results also have implications for other primary orders. In particular, a bilinear in the superconducting order parameter can couple linearly to odd-parity orders in centrosymmetric systems. Our findings open the door for exploring nonsymmorphic symmetries in the broader context of improper orders with potential applications to topological functional materials.
[1] A. Szabo, A. Ramires, arXiv:2309.05664