TORONTO, ON – Experimental atomic physicists have discovered there is a maximum amount of electrical resistance, or resistivity, that can result from collisions between electrons.
A team from the University of Toronto, L'École Normale Supérieure in Paris and Lehigh University in Pennsylvania studied ultracold potassium atoms cooled to near absolute zero. They found when increasing the rate at which atoms collide, the resulting resistance eventually stops increasing, offering new insights into what causes resistivity at the microscopic level.
"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."
The researchers used an optical lattice, a grid of light that traps atoms and lets them behave like electrons in a solid, to simulate extreme conditions that solids cannot reach. The highly controlled environment allowed the researchers to isolate the role of collisions.
"We observed that the atoms, which are only a few nanometres 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."
The team found that when the interactions between atoms became very strong, the resistivity caused by collisions eventually stopped rising and saturated. This suggests that the resistivity increase from electron-on-electron scattering in a metal would also be limited for similar reasons.
"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.
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