Illustration from Scientific Research

(001) monolayer of Bi 4 X 4 topological materials assembled by quasi-1D molecular chain as the building block along a axis by vdW force. The blue and gray balls represent Bi atoms and I/Br atoms, respectively. The schematics of the stacking mode along c axis and crystal structure of -Bi 4 I 4 , ’-Bi 4 I 4 , and Bi 4 Br 2 I 2 are shown in the orange dashed square. Each of the red, yellow, and blue parallel arrow represents one (001) plane of Bi 4 X 4 with the orientations and displacements.

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