Electrons stop acting like particles—and physics still works

Electrons stop acting like particles-and physics still works Even when electrons stop acting like particles, quantum materials can still unlock powerful topological states. Date: January 15, 2026 Source: Vienna University of Technology Summary: Physicists have long relied on the idea that electrons behave like tiny particles zipping through materials, even though quantum physics says their exact position is fundamentally uncertain. Now, researchers at TU Wien have discovered something surprising: a material where this particle picture completely breaks down can still host exotic topological states-features once thought to depend on particle-like behavior. Share: Quantum physics shows that particles do not behave like solid objects with fixed locations. Instead, they act more like waves, which means their exact position in space cannot be precisely known. Even so, in many everyday situations, scientists can still describe particles in a familiar, classical way. They picture them as tiny objects moving through space with a specific speed. This approach works well when explaining how electricity flows through metals. Physicists often describe electric current as electrons speeding through a material, pushed or redirected by electromagnetic forces as they move. Why the Particle Picture Usually Works Many modern theories also rely on this particle-based view, including the idea of topological states of matter. These states are so important that their discovery was recognized with the Nobel Prize in Physics in 2016. Despite their advanced mathematics, these theories still assume electrons behave like particles with defined motion. However, researchers have found that this picture does not apply to every material (see publication below). In some cases, electrons no longer behave like individual particles with a clear position or a single, well-defined velocity. Topology Without Particles Scientists at TU Wien have now demonstrated that even when the particle picture fails, materials can still display topological properties. Until now, these properties were thought to depend on particle-like behavior. This finding reveals something unexpected. Topological states are not limited to systems where electrons act like particles. Instead, these states turn out to be far more universal, bringing together ideas that once seemed incompatible. When the Particle Picture No Longer Makes Sense "The classical picture of electrons as small particles that suffer collisions as they flow through a material as an electric current is surprisingly robust," says Prof. Silke Bühler-Paschen from the Institute of Solid State Physics at TU Wien. "With certain refinements, it works even in complex materials where electrons interact strongly with one another." There are, however, extreme cases where this description breaks down entirely. In these situations, the charge carriers lose their particle-like nature. This behavior appears in a compound made of cerium, ruthenium and tin (CeRu4Sn6), which researchers at TU Wien studied at extremely low temperatures. "Near absolute zero, it exhibits a specific type of quantum-critical behavior," says Diana Kirschbaum, first author of the current publication. "The material fluctuates between two different states, as if it cannot decide which one it wants to adopt. In this fluctuating regime, the quasiparticle picture is thought to lose its meaning." Topology...

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