Photo-induced Critical Magnetization Dynamics in Magnetic Topological Insulator MnBi₂Te₄

We investigate the ultrafast magnetization dynamics of the antiferromagnetic topological insulator MnBi₂Te₄ (MBT) using time-resolved magneto-optical Kerr effect (trMOKE) measurements as a function of temperature, magnetic field, fluence, and polarization. MBT has generated substantial interest as the first intrinsic magnetic topological insulator, hosting topologically nontrivial states that may have applications to spintronics and quantum computing. Furthermore, theory predicts that the magnetic ground state of MBT lies in proximity to several competing orders due to frustration from large next-nearest neighbor AFM exchange [1] along with strong coupling between electronic [2], magnetic, and lattice degrees of freedom [3]. This opens the door for the optical control and engineering of nonequilibrium states of matter. Here, we characterize the photo-induced nonequilibrium dynamics across the phase diagram, building upon previous work [4]. We show that the dynamics are well defined across most of the phase diagram and exhibit critical behavior with metastable dynamics near the AFM-spin flop transition.

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[2] M. Köpf, J. Ebad-Allah, S.H. Lee, Z.Q. Mao, and C.A. Kuntscher Phys. Rev. B 102, 165139 (2020)

[3] H. Padmanabhan, M. Poore, P.K. Kim, et al., Nature communications 13 (1), 1-10 (2022)

[4] H. Padmanabhan, V.A. Stoica, P.K. Kim, M. Poore, ... Advanced Materials, 2202841 (2022)