Laser-hit magnet breaks physics rule, Oak Ridge lab finds

Scientists at Oak Ridge National Laboratory (ORNL) hit a magnetic material with rapid laser pulses and watched it with neutrons. The material broke a basic rule of physics called detailed balance, and it stayed in that state instead of quickly settling back, the laboratory announced on Nov. 9. The researchers say the long-lived signal could help quantum technologies that use magnetic excitations to carry and store information.ornl.gov

The results appeared in Nature Communications. A listing in ORNL's publication database shows the paper was published in April 2026, with Chengyun Hua, Barry Winn, Colin Sarkis, Gabriele Sala, Takeshi Egami and Alan Tennant as authors.ornl.gov

A lopsided signal that lasted

The team studied magnons. These are quasiparticles, wave-like ripples in a material's magnetic order that can carry information, according to ORNL's announcement. When a system is at rest, detailed balance ties energy-gaining and energy-losing events together in a predictable way. Under the laser pulses, that link failed, and the neutron data showed extra signals on only one side.newswise.com

The excess magnons did not fade away. That ruled out simple heating and pointed to a "long-lived nonequilibrium steady state sustained by periodic laser pulsing," the lab said. The paper's abstract says the material was a two-dimensional square-lattice Heisenberg antiferromagnet. It also argues that the violation reflects the quantum-mechanical nature of the system's dynamics, according to ORNL's publication summary.ornl.gov+1

"No one before has directly probed a detailed balance violation in a condensed matter system," Hua said in the ORNL release. "Theoretically it makes sense it can happen, but experimentally it was pretty awesome to see."newswise.com

Building a pump-probe beamline

Neutron scattering normally looks at materials in equilibrium. The team had to adapt ORNL's Spallation Neutron Source to work while a sample was being actively driven. An earlier technical paper by the group describes the setup on the HYSPEC spectrometer. It uses a nanosecond pulsed laser timed to the neutron pulses, along with Rb2MnF4, a quantum magnet in which magnons near the zone center can in theory last up to milliseconds.ar5iv.labs.arxiv.org

"Because we were taking a new approach, mechanics, safety personnel, hardware and software engineers, and the research team all had to think outside the box to make this project work," Hua said, according to the lab. The effort started with an ORNL seed grant. The Department of Energy's Office of Science and the Quantum Science Center supported the later work.ornl.gov

What comes next

ORNL says the system gives researchers a way to study other nonequilibrium quantum physics in real time. That work could inform research on coherent transport, memory devices and low-loss electronics, the lab said. The authors write that their in operando technique could be extended to one-dimensional spin chains and topological spin systems, "where nonequilibrium effects are widespread and rich in discovery potential," per the paper's abstract.ornl.gov+1