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

Abstract

In 1978, Wilczek and Weinberg theoretically discovered a new boson-the Axion-which is the coherent oscillation of the $\theta$ field in QCD. Its existence can solve multiple fundamental questions including the strong CP problem of QCD and the dark matter. However, its detection is challenging because it has almost no interaction with existing particles. Similar $\theta$ has been introduced to condensed matter and so far studied as a static, quantized value to characterize topology of materials. But the coherent oscillation of $\theta$ in condensed matter is proposed to lead to new physics directly analogous to the high-energy Axion particle, the dynamical Axion quasiparticle (DAQ). In this paper, we present the direct observation of the DAQ. By combining 2D electronic device with ultrafast pump-probe optics, we manage to measure the magnetoelectric coupling $\theta$ ($\theta \propto \alpha$) of 2D MnBi${}_2$Te${}_4$ with sub-picosecond time-resolution. This allows us to directly observe the DAQ by seeing a coherent oscillation of $\theta$ at ~44 GHz in real time, which is uniquely induced by the out-of-phase antiferromagnetic magnon. Interestingly, in 2D MnBi${}_2$Te${}_4$, the DAQ arises from the magnon-induced coherent modulation of Berry curvature. Such ultrafast control of quantum wavefunction can be generalized to manipulate Berry curvature and quantum metric of other materials in ultrafast time-scale. Moreover, the DAQ enables novel quantum physics such as Axion polariton and electric control of ultrafast spin polarization, implying applications in unconventional light-matter interaction and coherent antiferromagnetic spintronics. Beyond condensed matter, the DAQ can serve as a detector of the dark matter Axion particle. We estimate the detection frequency range and sensitivity in the critically-lacking meV regime, contributing to one of the most challenging questions in fundamental physics.

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Cited by in corpus (13)

• Intrinsic magnetic topological insulators of the MnBi${}_2$Te${}_4$ family
• Unlocking Quantum Control and Multi-Order Correlations via Terahertz Two-Dimensional Coherent Spectroscopy
• Intrinsic Layer-Dependent Surface Energy and Exfoliation Energy of van der Waals Materials
• Analytical model of a Tellegen meta-atom
• Ferroelectric switching of quantum anomalous Hall effects in MnBi2Te4 films
• Strongly enhanced topological quantum phases in dual-surface AlO${}_x$-encapsulated MnBi${}_2$Te${}_4$
• Probing dynamical axion quasiparticles with two-photon correlations
• Axions at the meV Crossroads: Theory, Cosmology, Astrophysics, and Experiments
• Chromium chalcohalide Janus monolayer ferromagnets with perpendicular magnetic anisotropy and high Curie temperature
• Theoretical design of the large topological magnetoelectric effect in the Co-intercalated NbS${}_2$ structure
• Research on topological materials using ultrafast spectroscopy
• Emerging axion detection in artificial magnetoelectric materials
• Quantum Semiconductor Heterostructures for meV Axion Dark Matter Detection