Using circularly-polarized light to control quantum matter is a highly intriguing topic in physics, chemistry and biology. Antiferromagnets (AFMs) have zero net magnetization, so AFM domains are immune to perturbing magnetic field. This leads to the prospect of robust magnetic storage. However, this robustness also means that manipulating fully-compensated AFM order is extremely difficult. We report the surprising observation of helicity-dependent optical control of fully compensated antiferromagnetic (AFM) order in 2D even-layered MnBi2Te4, a topological Axion insulator no magnetization. We demonstrated helicity-dependent optical creation of AFM domain walls by double induction beams and the direct reversal of AFM domains by ultrafast pulses. The control and reversal of AFM domains and domain walls by light helicity have never been achieved in any fully-compensated AFM. To understand this optical control, we studied an AFM circular dichroism (CD) proportional to the AFM order, which only appears in reflection but is absent in transmission. We showed that the optical control and CD both arise from the optical Axion electrodynamics. The Axion induction provides the possibility to optically control a family of PT-symmetric AFMs such as Cr2O3, even-layered CrI3, and possibly pseudo-gap state in cuprates.

Reference:
J. Qiu, et al. “Axion optical induction of antiferromagnetic order” Nature Materials s41563-023-01493-5 (2023).

Bio: Suyang Xu received PhD in the Physics Department of Princeton University under the supervision of Prof. M. Zahid Hasan. During his phd, Xu experimentally realized a wide range of new topological phases of matter, including the discovery of the Weyl semimetal in the TaAs class of material, which was selected as a top10 breakthrough in physics in 2015. In 2016, Xu moved to MIT Physics for postdoc under the supervision of Prof. Nuh Gedik. There, Xu pioneered in nonlinear optical studies of topological materials including photocurrents, nonlinear Hall and second-harmonic generation. In 2020, Xu started his independent career in the department of Chemistry and Chemical Biology at Harvard as an assistant professor.