Every time electricity flows through a wire, some of its energy is inevitably lost as heat because electrons collide with one another and with the material around them. But just how much can these collisions increase electrical resistance? A new study suggests there is a fundamental limit.

To investigate, researchers from the University of Toronto, L’École Normale Supérieure in Paris, and Lehigh University turned to an unusual stand-in for electrons: ultracold potassium atoms cooled to temperatures just above absolute zero.

By precisely controlling how often the atoms collided, they found that resistance increased only up to a certain point before leveling off. The discovery provides rare experimental evidence for a microscopic limit to resistivity and could improve scientists’ understanding of electron behavior in quantum materials.

“Electron-on-electron collisions are known to increase resistivity in some pure materials,” explains Professor Joseph Thywissen in the Department of Physics and the Center for Quantum Information and Quantum Control in the Faculty of Arts & Science at the University of Toronto, senior author of a study published in Physical Review Letters. “The energy produced by electrical resistance shows up as heat. Transmission lines, for instance, lose up to 8% of the generated electrical power. Resistivity is also interesting to study because it can be a signature of new physics in materials.”