Exploring intrinsic magnetic topological insulators: The case ofEuIn2⁢As2

In this paper, ultrafast optical spectroscopy was employed to elucidate the intricate topological features of EuIn2⁢As2, a promising candidate for a magnetic topological crystalline axion insulator. Our investigation has revealed the exceptional sensitivity of the ultrafast carrier dynamics to the antiferromagnetic phase transition (𝑇𝑁≈16 K). Below 𝑇𝑁, two distinct, extremely low-energy collective modes, 𝜔1 and 𝜔2, with frequencies of ∼9.9 and 21.6 GHz at 𝑇=4 K, respectively, were observed, exhibiting strong temperature dependence. The higher-frequency mode is a magnon, and the lower-frequency mode, whose origin is currently uncertain, cannot be attributed to a coherent acoustic phonon. Additionally, high-fluence photoexcitation suggests the possibility of light-induced nonthermal phase transitions, such as the disruption of antiferromagnetic order. These findings provide insights into the interplay between topology and magnetism in EuIn2⁢As2, making it a promising candidate for applications in quantum information and spintronics.