Observation of the Axion quasiparticle in 2D MnBi$_2$Te$_4$

In a recent study, researchers including Berkeley-Riken fellow Jan Schütte-Engel report a groundbreaking discovery in a material known as MnBi_2Te_4. They found direct evidence for what’s called a dynamical axion quasiparticle (DAQ), a coherent spin wave oscillation in the material that closely resembles the elusive axion particle predicted in high-energy physics. Particle physics axions, if found, could help explain puzzling mysteries like dark matter and a symmetry issue in particle physics called the strong CP problem. In the new study, the team used ultrafast “pump–probe” laser techniques to detect the DAQ.

Particle physics axions have never been directly observed. The discovery of the DAQ opens exciting opportunities for both fundamental physics and future technologies. On the fundamental physics side, such materials could help in the detection of dark matter axions. The authors have calculated the sensitivity of these newly discovered DAQ for dark matter axion searches. On the technological side, precise control of the dynamic quantum properties may lead to novel sensors, high-speed electronics, and quantum devices.