It is generally believed that topological insulators are highly immune to non-magnetic defects, but there is still a lack of verification on a mesoscopic scale of device applications. We take SiSnF2 monolayer ribbons as an illustration to study the effects of defects and sizes on the electron transport in topological insulators. First-principles calculations show that SiSnF2 is transformed into a topological insulator under a tensile strain greater than 2%. The data of an effective tight-binding model are obtained by using a genetic algorithm to calculate the transport properties of the topological insulator SiSnF2 ribbons, and it is found that edge states can also be disrupted by random vacancy defects. For a ribbon with a length of 18.8 nm and a width of 8.2 nm, when it has no defects, the current is concentrated at its edge, and its conductance is an ideal value of the topological edge state, 2e2/h. When the defect concentration is 1%, the edge current is appreciably disturbed, but the backscattering is still effectively suppressed, and the current bypasses the defect and still goes forward. When the concentration is 5%, the edge electrons are scattered deep into the ribbon and scattered with the opposite edge, destroying the topological edge state and reducing the conductance to 0.6e2/h. Therefore, the transformation from topological to normal insulator caused by defects happens gradually rather than suddenly. Found in this study is an obvious transport quantum size effect, i.e. increasing the ribbon width can reduce electron scattering between edges and enhance the stability of topological edge states; while increasing the length will increase electron localization and electron scattering between edges, reducing the stability of topological edge states.
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2025年第74卷第6期066401补充材料.pdf
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