Electrons stop acting like particles and topological effects remain

Researchers at TU Wien report that a cerium–ruthenium–tin compound (CeRu4Sn6) shows topological behavior even when electrons lose particle-like character, and experiments at temperatures near absolute zero revealed a spontaneous (anomalous) Hall effect without an external magnetic field.

Researchers at TU Wien report that a crystalline compound made of cerium, ruthenium and tin shows topological behavior even when electrons no longer behave like individual particles. The material, CeRu4Sn6, was studied at temperatures close to absolute zero where it exhibits quantum-critical fluctuations. Experimental work detected a spontaneous (anomalous) Hall effect in the absence of an external magnetic field. Theoretical collaborators at Rice University developed a model linking quantum criticality with topology to help explain the observations. Key findings: - In CeRu4Sn6, charge carriers lose their usual particle-like description in a quantum-critical regime at very low temperatures. - Despite the absence of well-defined quasiparticles, the material displays a spontaneous (anomalous) Hall effect without an applied magnetic field. - The observed topological signal is strongest where quantum fluctuations are largest and disappears when those fluctuations are suppressed by pressure or magnetic fields. - The phase is described by the authors as an emergent topological semimetal, indicating topology can arise beyond particle-based descriptions. - A theoretical model from collaborators at Rice University links quantum criticality with the emergence of topological properties. Summary: The study indicates that topological distinctions can emerge even when the usual particle picture of electrons breaks down, expanding how topological matter can be defined. The researchers report that the topological effect correlates with quantum-critical fluctuations and that those properties vanish when fluctuations are suppressed. They propose that focusing on quantum-critical materials may reveal additional emergent topological systems.