Applied Physics

TI Tuning

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Science  14 Oct 2011:
Vol. 334, Issue 6053, pp. 158
DOI: 10.1126/science.334.6053.158-c

On the list of exotic materials on the verge of becoming technologically useful, topological insulators (TIs) rank high. They possess a favorable electronic surface state in which a certain type of scattering is suppressed because of symmetry; however, in almost all materials identified to date, this surface state is barely noticeable in comparison with the dominant but conventionally conducting bulk state. Chemical doping and electrical gating have been used to control the conductivity of the bulk state in binary TIs such as Bi2Se3. With the same aim, Kong et al. vary the Bi and Sb content in thin nanoplates of a ternary compound (BixSb1-x)2Te3 between the two extremes, Bi2Te3 and Sb2Te3, which are both TIs. They find that the TI character is maintained across the doping range, while the carrier density of the bulk state varies dramatically in magnitude, reaching a minimum at equal amounts of Bi and Sb (x = 0.5). For this optimal composition and at an optimal thickness of the plate, applying a gate voltage leads to pronounced tuning of the carrier density and type, going from electron- to hole-dominated transport, similar to what has been observed in graphene.

Nat. Nanotechnol. 10.1038/NNANO.2011.172 (2011).

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