Fig. 4. Evolution of polaronic effect across the magnetic phase transition from the layered AFM to FM in bilayer CrI₃.

a Raman spectra of bilayer CrI₃ acquired at 10 K in the circularly parallel polarization channels, RR and LL, where RR (LL) stands for that both incident and scattered polarizations are selected to be right-handed (left-handed) circularly polarized, with an applied out-of-plane magnetic field ($B_{\perp }$) of 1 T (top), 0 T (middle), and −1 T (bottom), respectively. b, c Plots of the Poisson fit amplitude $A_0$ (b) and electron–phonon coupling strength ${\alpha }_{2\mathrm{D}}$ (c) as a function of the applied $B_{\perp }$ in RR (orange data points) and LL (blue) channels. Solid lines are step (orange and blue in b) and linear (gray in c) function fits to the magnetic field dependence of $A_0$ and ${\alpha }_{2\mathrm{D}}$, respectively. Error bars are defined as one standard error of the fitting parameters.