Extended Data Fig. 3: Raman spectroscopy of exfoliated and bulk α-Bi4Br4.
a, Raman spectrum obtained from a mechanically exfoliated α-Bi4Br4 flake consisting of four atomic layers. The inset shows an optical microscopy image of the corresponding α-Bi4Br4 flake on a SiO2/Si substrate, with the flake boundary outlined by a white dashed rectangle. b, Raman spectrum of bulk α-Bi4Br4, accompanied by the corresponding optical microscopy image in the inset. The Raman shift acquired from the four-layer flake matches the bulk Raman shift, indicating the preservation of the crystalline properties throughout the exfoliation process. The error bar associated with peak identification is approximately 1 cm−1.
