Researchers from the University of Toronto, L'École Normale Supérieure in Paris and Lehigh University in Pennsylvania reached the finding by studying ultracold potassium atoms cooled to nearly absolute zero. As the scientists increased the frequency of collisions between the atoms, resistance initially rose. Beyond a certain point, however, it stopped climbing.

The result offers a more detailed view of how resistivity develops at the microscopic level.

Why Electrical Resistance Matters

"Electron-on-electron collisions are known to increase resistivity in some pure materials," explains Professor Joseph Thywissen in the Department of Physics and the Centre 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 eight per cent of generated electrical power. Resistivity is also interesting to study because it can be a signature of new physics in materials."

To investigate these collisions under tightly controlled conditions, the team used an optical lattice. This grid of light traps atoms and allows them to mimic the behavior of electrons moving through a solid.

The setup made it possible to recreate extreme conditions that ordinary solid materials cannot reach while isolating the effects of particle collisions.

Ultracold Atoms Mimic Electrons

"We observed that the atoms, which are only a few nanometers in size, bump into each other as if they were much larger," says Thywissen. "This quantum enhancement of the effective atom size makes collisions on a given lattice site much more likely, increasing the resistivity of the system."

As the interactions grew stronger, collision-driven resistivity eventually leveled off instead of continuing to rise. The researchers say this saturation suggests that electron collisions in a metal may also face a similar upper limit.

A New Window Into Quantum Materials

The findings provide a clearer microscopic explanation for how resistance behaves in low-density metals. They may also help guide future research into strongly correlated atomic systems and quantum materials, where particles interact in unusually complex ways.

"Our results provide a clear microscopic understanding of how resistivity works in low-density metals and open the door to new studies of strongly correlated atomic systems and quantum materials," says Thywissen.