Oak Ridge National Laboratory Team Observes a Long-Lived Nonequilibrium Quantum State in a Magnetic Material: Laser-Driven Magnons Violate Detailed Balance, Published in Nature Communications
Researchers at the Department of Energy Oak Ridge National Laboratory and their collaborators have observed a long-lived quantum state in a magnetic material, in findings published in Nature Communications. The team used rapid laser pulses to drive the material out of its normal resting state and used neutron scattering to study the microscopic details of its magnetic behavior.
The team studied magnons, quantum quasiparticles whose wavelike excitations are critical to magnetic behavior in materials. The neutron measurements were made at the Spallation Neutron Source, a DOE Office of Science user facility, in a combined approach the release described as not typically used for nonequilibrium studies.
The measurements showed that the material violated a physical rule called detailed balance. In a system at rest, detailed balance links energy-gaining and energy-losing events in a predictable way; under the rapid laser pulses, that balance broke, and the neutron data showed extra signals only on one side.
The nonequilibrium state also did not quickly disappear. The lopsided excess magnons persisted, indicating that the team was seeing a long-lived nonequilibrium steady state sustained by periodic laser pulsing rather than a brief heating effect.
Chengyun Hua of Oak Ridge National Laboratory said no one before has directly probed a detailed balance violation in a condensed matter system, and that while it makes theoretical sense, seeing it experimentally was remarkable.
The team said the observation makes the system a strong platform for studying other nonequilibrium quantum physics in real time, and gives scientists a new benchmark for what neutron scattering can reveal when materials are observed while actively driven.
来源： https://phys.org/news/2026-11-laser-driven-magnetic-state-defies.html
Published by GSM · USA (original Chinese edition)
Photo: Wikipedia/Wikimedia Commons 词条主图：Oak Ridge, Tennessee
