Fig. 2

Detection of the zero-momentum magnons in thick CrI₃. a Raman spectra of a thick CrI₃ flake (13 layers) at low temperature (10 K) in the parallel and cross-channels at ϕ = 0^o (XX and XY) and at ϕ = 45^o (X’X’ and X’Y’). Magnon modes, M₁ and M₂, appearing only in the cross-channels (XY and X’Y’), are highlighted in yellow and blue. Phonon modes are labeled as A₁, A₂, E₁–E₄, and A₃. The spectral intensities in the 70–120 cm^–1 range are multiplied by a factor of 10. The spectra in the XX and XY channels are vertically offset for clarity. The spectra are acquired using a 633-nm excitation laser. b, c Temperature dependence of I. I. of the M₁ and M₂ magnon modes, respectively. Solid curves are fits to \(I_0 + I\sqrt {T_{\mathrm{C}} - T}\). d, e Temperature dependence of the lifetime (Γ⁻¹, left axis) and the linewidth (Γ, right axis) of the M₁ and M₂ magnon modes, respectively. Error bars in b–e represent the two standard errors of fitting parameters in the Lorentzian fits to individual temperature-dependent Raman spectra