Magnons and magnetic fluctuations in atomically thin MnBi2Te4

Date
2022-05-09
Authors
Lujan, David
Choe, Jeongheon
Rodriguez-Vega, Martin
Ye, Zhipeng
Leonardo, Aritz
Nunley, T, Nathan
Chang, Liang-Juan
Lee, Shang-Fan
Yan, Jiaqiang
Fiete, Gregory A.
Journal Title
Journal ISSN
Volume Title
Publisher
Springer Nature Limited
Abstract

Electron band topology is combined with intrinsic magnetic orders in MnBi2Te4, leading to novel quantum phases. Here we investigate collective spin excitations (i.e. magnons) and spin fluctuations in atomically thin MnBi2Te4 flakes using Raman spectroscopy. In a two- septuple layer with non-trivial topology, magnon characteristics evolve as an external mag- netic 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.

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Citation
Lujan, D; Choe, J; Rodriguez-Vega, M; Ye, ZP; Leonardo, A; Nunley, TN; Chang, LJ; Lee, SF; Yan, JQ; Fiete, GA; He, R; Li, XQ. Magnons and magnetic fluctuations in atomically thin MnBi2Te4. Nat. Commun. 2022, 13(1), 2527-. DOI: 10.1038/s41467-022-29996-w.