Topological semimetal driven by strong correlations and crystalline symmetry

Electron correlations amplify quantum fluctuations and, as such, are recognized as the origin of many quantum phases. However, whether strong correlations can lead to gapless topological states is an outstanding question, in part because many of the ideas in topological condensed-matter physics rely on the analysis of an effectively non-interacting band structure. Therefore, a framework that allows the identification of strongly correlated topological materials is needed. Here we suggest a general approach in which strong correlations cooperate with crystalline symmetry to drive gapless topological states. We test this materials design principle by exploring Kondo lattice models and materials whose space-group symmetries promote different kinds of electronic degeneracies. This approach allows us to identify Weyl–Kondo nodal-line semimetals with nodes pinned to the Fermi energy, demonstrating that it can be applied to discover strongly correlated topological semimetals. We identify three heavy-fermion compounds as material candidates, provide direct experimental evidence for our prediction in Ce₂Au₃In₅ and discuss how our approach may lead to many more. Our findings illustrate the potential of this materials design principle to guide the search for new topological metals in a broad range of strongly correlated systems.