"Weak anti-localization in Bi2 (SexTe1-x) 3 nanoribbons and nanoplates"

Judy J. Cha: Desheng Kong, Seung-Sae Hong, James G. Analytis, Keji Lai, Yi Cui; Nano Letters, 01/20/12.

Additional Authors: Desheng Kong, Seung-Sae Hong, James G. Analytis, Keji Lai, Yi Cui

Abstract:

Studying the surface states of Bi2Se3 and Bi2Te3 topological insulators has proven challenging due to the high bulk carrier density that masks the surface states. Ternary compound Bi2(SexTe1–x)3 may present a solution to the current materials challenge by lowering the bulk carrier mobility significantly. Here, we synthesized Bi2(SexTe1–x)3 nanoribbons and nanoplates via vapor–liquid–solid and vapor–solid growth methods where the atomic ratio x was controlled by the molecular ratio of Bi2Se3 to Bi2Te3 in the source mixture and ranged between 0 and 1. For the whole range of x, the ternary nanostructures are single crystalline without phase segregation, and their carrier densities decrease with x. However, the lowest electron density is still high (1019 cm–3) and the mobility low, suggesting that the majority of these carriers may come from impurity states. Despite the high carrier density, weak antilocalization (WAL) is clearly observed. Angle-dependent magnetoconductance study shows that an appropriate magnetic field range is critical to capture a true, two-dimensional (2D) WAL effect, and a fit to the 2D localization theory gives α of −0.97, suggesting its origin may be the topological surface states. The power law dependence of the dephasing length on temperature is T–0.49 within the appropriate field range (0.3 T), again reflecting the 2D nature of the WAL. Careful analysis on WAL shows how the surface states and the bulk/impurity states may interact with each other.