• Axion quasiparticles were observed for the first time in a two-dimensional quantum material (MnBi2Te4), a topological antiferromagnet.
• The experiment used ultrafast pump-probe spectroscopy to detect coherent oscillations, providing evidence for the axion quasiparticle.
• The discovery could lead to new methods for detecting dark matter and applications in ultrafast antiferromagnetic spintronics.

Physicists have successfully observed axion quasiparticles within a two-dimensional quantum material, manganese bismuth telluride (MnBi2Te4). This topological antiferromagnet exhibits unique properties that allow for the creation and observation of these quasiparticles. The experiment, led by Jianxiang Qiu of Harvard University, utilized ultrafast pump-probe spectroscopy to detect the coherent oscillations associated with the axion quasiparticle. This discovery offers a new approach to understanding axions, a leading candidate for dark matter, and may lead to advancements in spintronics.

• What: Observation of axion quasiparticles in a topological antiferromagnet (MnBi2Te4) using ultrafast pump-probe spectroscopy.
• Who: Jianxiang Qiu (Harvard University) and colleagues.
• When: Research published in Nature, reported on May 2, 2025.
• Where: Harvard University (research location); experiments conducted on two-dimensional layers of MnBi2Te4.

The observation of axion quasiparticles in MnBi2Te4 represents a significant step forward in the search for dark matter and the development of new spintronic technologies. The use of a topological antiferromagnet and ultrafast spectroscopy allowed researchers to detect the elusive quasiparticles. This new approach could provide a more accessible and cost-effective method for studying axions compared to traditional high-energy physics experiments. The potential to create axion-polaritons and explore applications in ultrafast antiferromagnetic spintronics further highlights the importance of this discovery.

This is uniquely enabled by the out-of-phase magnon in this topological material. Such coherent oscillations are the smoking-gun evidence for the axion quasiparticle and it is the combination of topology and magnetism in MnBi2Te4 that gives rise to it.

The detection of axion quasiparticles in a topological antiferromagnet provides a promising new avenue for exploring the properties of axions and their potential role in dark matter. The experiment demonstrates the power of condensed-matter physics in addressing fundamental questions in particle physics. Future research will focus on developing new axion detectors and exploring applications in spintronics, potentially leading to significant advancements in both fields.