Title: Distinguishing Surface and Bulk Electromagnetism via Their Dynamics in an Intrinsic Magnetic Topological Insulator Show Chinese title

Title: 通过内在磁性拓扑绝缘体中的动力学区分表面和体电磁学

Abstract: The indirect exchange interaction between local magnetic moments via surface electrons has been long predicted to bolster the surface ferromagnetism in magnetic topological insulators (MTIs), which facilitates the quantum anomalous Hall effect. This unconventional effect is critical to determining the operating temperatures of future topotronic devices. However, the experimental confirmation of this mechanism remains elusive, especially in intrinsic MTIs. Here we combine time-resolved photoemission spectroscopy with time-resolved magneto-optical Kerr effect measurements to elucidate the unique electromagnetism at the surface of an intrinsic MTI MnBi2Te4. Theoretical modeling based on 2D Ruderman-Kittel-Kasuya-Yosida interactions captures the initial quenching of a surface-rooted exchange gap within a factor of two but over-estimates the bulk demagnetization by one order of magnitude. This mechanism directly explains the sizable gap in the quasi-2D electronic state and the nonzero residual magnetization in even-layer MnBi2Te4. Furthermore, it leads to efficient light-induced demagnetization comparable to state-of-the-art magnetophotonic crystals, promising an effective manipulation of magnetism and topological orders for future topotronics. Show Chinese abstract

Abstract: 通过表面电子间接交换相互作用来增强磁性拓扑绝缘体（MTI）中的表面铁磁性早已被预测，这有助于量子反常霍尔效应。 这种非传统效应对于决定未来拓扑电子器件的运行温度至关重要。 然而，这一机制的实验验证仍然难以实现，特别是在本征MTI中更是如此。 在这里，我们结合时间分辨光电子能谱与时间分辨磁光克尔效应测量，阐明了本征MTI MnBi₂Te₄表面的独特电磁性质。 基于二维Ruderman-Kittel-Kasuya-Yosida相互作用的理论模型在两个数量级内捕获了表面起源的交换间隙的初始淬灭，但高估了体相去磁一个数量级。 此机制直接解释了准二维电子态中的大间隙以及偶数层MnBi₂Te₄中的非零剩余磁化。 此外，它还导致了高效的光诱导去磁，其效果可与最先进的磁光晶体相比，有望有效操控未来拓扑电子学中的磁性和拓扑序。