Magnetic Topological Insulator MnBi₂Te₄ Nanosheets for Femtosecond Pulse Generation

The van der Waals layered material MnBi₂Te₄, as a magnetic topological insulator, has attracted tremendous interest for novel physics research in the fields of condensed matter physics and materials science. However, the nonlinear optical properties of MnBi₂Te₄ and its applications in ultrafast optics have rarely been explored. In this study, high-quality MnBi₂Te₄ nanosheets have been successfully synthesized by the self-flux method. The morphology, chemical composition, magnetic properties, and nonlinear optical characteristics were systematically investigated. The magnetic transition of MnBi₂Te₄ was confirmed by a low-temperature spatially resolved spectroscopic technique. The saturable absorption property of MnBi₂Te₄ was measured by a balanced twin-detector system with a modulation depth of 4.5% and a saturation optical intensity of 2.35 GW/cm². Furthermore, by inserting the MnBi₂Te₄-based saturable absorber, a soliton mode-locking laser operating at 1558.8 nm was obtained with a pulse duration of 331 fs. This research will pave the way for applications of the magnetic TI MnBi₂Te₄ in nonlinear optics and photonics.