Optical signatures of Euler superconductors

Abstract: We study optical manifestations of multigap band topology in multiband superconductors with a non-trivial topological Euler class. We introduce a set of lattice models for non-Abelian superconductors with the Euler invariant signified by a non-trivial quantum geometry. We then demonstrate that the topological Bogoliubov excitations realized in these models provide for a characteristic first-order optical response distinct from those of the other known topological superconductors. We find that the spectral distribution of the optical conductivity universally admits a topologically quantized jump and naturally differs from the features induced by the quantum geometry in the non-interacting bands without pairing terms. Further to uncovering observable signatures in first-order optical conductivities, we showcase that the higher-order nonlinear optical responses of the non-Abelian Euler superconductor can result in enhanced steady dc currents that fingerprint the exotic topological invariant. Finally, by employing a diagrammatic approach, we generalize our findings beyond the specific models of Euler superconductors.