• Axion quasiparticles have been observed for the first time in a topological antiferromagnet (MnBi2Te4).
• The discovery utilizes a new detection strategy based on quasiparticles as axion 'simulators'.
• The research could lead to new axion dark matter detectors and applications in ultrafast antiferromagnetic spintronics.

Physicists led by Jianxiang Qiu at Harvard University have successfully observed axion quasiparticles within a two-dimensional quantum material, specifically manganese bismuth telluride (MnBi2Te4), a topological antiferromagnet. This breakthrough utilizes the material's unique properties to simulate axions, hypothetical particles considered a leading candidate for dark matter. The experiment involved applying a static magnetic field and bombarding the material with sub-picosecond light pulses, a technique called ultrafast pump-probe spectroscopy, leading to the observation of coherent oscillations indicative of axion quasiparticles. This discovery offers a new pathway for dark matter detection and potential advancements in spintronics.

• What: Observation of axion quasiparticles, condensed-matter analogues of axions, in a topological antiferromagnet (MnBi2Te4) using ultrafast pump-probe spectroscopy.
• Who: Jianxiang Qiu (Harvard University) and colleagues.
• When: Research published in May 2025 (article published May 2, 2025).
• Where: Harvard University (research location).

The observation of axion quasiparticles in MnBi2Te4 represents a significant step forward in the search for dark matter. The use of a topological antiferromagnet and the application of ultrafast pump-probe spectroscopy provided a novel approach to detect these elusive particles. The potential for creating axion-polaritons and developing new types of dark matter detectors highlights the far-reaching implications of this research. However, the technical challenges related to materials engineering, specifically growing high-quality large crystals of MnBi2Te4, need to be addressed to fully realize the potential 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 successful observation of axion quasiparticles in a topological antiferromagnet provides a promising new avenue for dark matter research and potential applications in spintronics. While challenges remain in terms of materials engineering, the discovery offers a cost-effective alternative to high-energy physics experiments for axion detection. Future research will focus on hybridizing these quasiparticles with other particles, such as photons, to further explore their properties and potential applications.