Magnons and magnetic fluctuations in atomically thin MnBi2Te4

David Lujan; Jeongheon Choe; Martin Rodriguez-Vega; Zhipeng Ye; Aritz Leonardo; T Nathan Nunley; Liang-Juan Chang; Shang-Fan Lee; Jiaqiang Yan; Gregory A Fiete; Rui He; Xiaoqin Li

doi:10.1038/s41467-022-29996-w

Magnons and magnetic fluctuations in atomically thin MnBi₂Te₄

Nat Commun. 2022 May 9;13(1):2527. doi: 10.1038/s41467-022-29996-w.

Authors

David Lujan^#^{1

2}, Jeongheon Choe^#^{1

2}, Martin Rodriguez-Vega³, Zhipeng Ye⁴, Aritz Leonardo^{5

6}, T Nathan Nunley^{1

2}, Liang-Juan Chang^{1

7}, Shang-Fan Lee⁷, Jiaqiang Yan⁸, Gregory A Fiete^{9

10}, Rui He¹¹, Xiaoqin Li^{12

13}

Affiliations

¹ Department of Physics and Center for Complex Quantum Systems, The University of Texas at Austin, Austin, TX, 78712, USA.
² Center for Dynamics and Control of Materials and Texas Materials Institute, The University of Texas at Austin, Austin, TX, 78712, USA.
³ Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA. rodriguezvega.physics@gmail.com.
⁴ Department of Electrical and Computer Engineering, Texas Tech University, Lubbock, TX, 79409, USA.
⁵ Donostia International Physics Center, Paseo Manuel de Lardizabal 4, 20018, San Sebastian, Spain.
⁶ EHU Quantum Center, Universidad del País Vasco/Euskal Herriko Unibertsitatea UPV/EHU, 48940, Leioa, Spain.
⁷ Institute of Physics, Academia Sinica, Taipei, 11529, Taiwan.
⁸ Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
⁹ Department of Physics, Northeastern University, Boston, MA, 02115, USA.
¹⁰ Department of Physics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
¹¹ Department of Electrical and Computer Engineering, Texas Tech University, Lubbock, TX, 79409, USA. rui.he@ttu.edu.
¹² Department of Physics and Center for Complex Quantum Systems, The University of Texas at Austin, Austin, TX, 78712, USA. elaineli@physics.utexas.edu.
¹³ Center for Dynamics and Control of Materials and Texas Materials Institute, The University of Texas at Austin, Austin, TX, 78712, USA. elaineli@physics.utexas.edu.

^# Contributed equally.

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 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.

Grants and funding

F-1662/Welch Foundation