Figure 68.

(a) Top: Schematic illustrating IETS mechanism. Bottom: Color plot of IETS spectra (|(d²I)/(dV²)| versus V) taken on bilayer CrI₃ as a function of out-of-plane magnetic field (easy axis) shows two dispersing magnon modes. Bottom panel adapted with permission from ref (120). Copyright 2019 National Academy of Sciences of the United States of America. (b) Top: Spin-wave calculations of magnon dispersion in 2D CrI₃ from anisotropic Heisenberg model with nearest-neighbor interactions. Adapted with permission from 217. Copyright 2018 Springer Nature. Magnon energies are shown at high-symmetry Γ and M points as a function of nearest-neighbor exchange energy J and anisotropy α. Zoom-in of the acoustic branch at the Γ point shows an energy gap for α > 1. (c) Extracted J and α values for all three 2D chromium trihalides from IETS measurements.