Qiu Jian-Xiang, Ghosh Barun, Schütte-Engel Jan, Qian Tiema, Smith Michael, Yao Yueh-Ting, Ahn Junyeong, Liu Yu-Fei, Gao Anyuan, Tzschaschel Christian, Li Houchen, Petrides Ioannis, Bérubé Damien, Dinh Thao, Huang Tianye, Liebman Olivia, Been Emily M, Blawat Joanna M, Watanabe Kenji, Taniguchi Takashi, Fong Kin Chung, Lin Hsin, Orth Peter P, Narang Prineha, Felser Claudia, Chang Tay-Rong, McDonald Ross, McQueeney Robert J, Bansil Arun, Martin Ivar, Ni Ni, Ma Qiong, Marsh David J E, Vishwanath Ashvin, Xu Su-Yang
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA.
Department of Physics, Northeastern University, Boston, MA, USA.
Nature. 2025 May;641(8061):62-69. doi: 10.1038/s41586-025-08862-x. Epub 2025 Apr 16.
The axion is a hypothetical fundamental particle that is conjectured to correspond to the coherent oscillation of the θ field in quantum chromodynamics. Its existence would solve multiple fundamental questions, including the strong CP problem of quantum chromodynamics and dark matter, but the axion has never been detected. Electrodynamics of condensed-matter systems can also give rise to a similar θ, so far studied as a static, quantized value to characterize the topology of materials. Coherent oscillation of θ in condensed matter has been proposed to lead to physics directly analogous to the high-energy axion particle-the dynamical axion quasiparticle (DAQ). Here we report the observation of the DAQ in MnBiTe. By combining a two-dimensional electronic device with ultrafast pump-probe optics, we observe a coherent oscillation of θ at about 44 gigahertz, which is uniquely induced by its out-of-phase antiferromagnetic magnon. This represents direct evidence for the presence of the DAQ, which in two-dimensional MnBiTe is found to arise from the magnon-induced coherent modulation of the Berry curvature. The DAQ also has implications in light-matter interaction and coherent antiferromagnetic spintronics, as it might lead to axion polaritons and electric control of ultrafast spin polarization. Finally, the DAQ could be used to detect axion particles. We estimate the detection frequency range and sensitivity in the millielectronvolt regime, which has so far been poorly explored.
轴子是一种假设的基本粒子，据推测它对应于量子色动力学中θ场的相干振荡。它的存在将解决多个基本问题，包括量子色动力学的强CP问题和暗物质问题，但轴子从未被探测到。凝聚态物质系统的电动力学也能产生类似的θ，迄今为止它被作为一个静态的、量子化的值来研究，以表征材料的拓扑结构。有人提出，凝聚态物质中θ的相干振荡会导致与高能轴子粒子直接类似的物理现象——动态轴子准粒子（DAQ）。在此，我们报告在MnBiTe中观测到DAQ。通过将二维电子器件与超快泵浦-探测光学技术相结合，我们观测到θ在约44吉赫兹处的相干振荡，这是由其反相反铁磁磁振子独特地诱导产生的。这代表了DAQ存在的直接证据，在二维MnBiTe中发现DAQ源于磁振子诱导的贝里曲率相干调制。DAQ在光与物质相互作用和相干反铁磁自旋电子学中也有意义，因为它可能导致轴子极化激元和超快自旋极化的电控制。最后，DAQ可用于探测轴子粒子。我们估计了毫电子伏特量级的探测频率范围和灵敏度，这一范围迄今探索较少。
