%ALujan, David%AChoe, Jeongheon%ARodriguez-Vega, Martin%AYe, Zhipeng%ALeonardo, Aritz%ANunley, T.%AChang, Liang-Juan%ALee, Shang-Fan%AYan, Jiaqiang%AFiete, Gregory%AHe, Rui%ALi, Xiaoqin%BJournal Name: Nature Communications; Journal Volume: 13; Journal Issue: 1 %D2022%I %JJournal Name: Nature Communications; Journal Volume: 13; Journal Issue: 1 %K %MOSTI ID: 10325072 %PMedium: X %TMagnons and magnetic fluctuations in atomically thin MnBi2Te4 %XAbstract Electron band topology is combined with intrinsic magnetic orders in MnBi 2 Te 4 , leading to novel quantum phases. Here we investigate collective spin excitations (i.e. magnons) and spin fluctuations in atomically thin MnBi 2 Te 4 flakes using Raman spectroscopy. In a two-septuple layer with non-trivial topology, magnon characteristics evolve as an external magnetic field tunes the ground state through three ordered phases: antiferromagnet, canted antiferromagnet, and ferromagnet. The Raman selection rules are determined by both the crystal symmetry and magnetic order while the magnon energy is determined by different interaction terms. Using non-interacting spin-wave theory, we extract the spin-wave gap at zero magnetic field, an anisotropy energy, and interlayer exchange in bilayers. We also find magnetic fluctuations increase with reduced thickness, which may contribute to a less robust magnetic order in single layers. %0Journal Article