The momentum and spin of electrons in the topological insulators are constrained to be perpendicular due to strong spin-orbit coupling. This unique coupling between current and spin-polarization may enable a host of devices impossible with other semiconductor materials. However, only electrons within a few nanometers of the surface possess this so-called spin-momentum locking.
Our group is pursuing topological insulator surface states by synthesizing nanowires of Bi2Se3 and Bi2Te3 with thicknesses of only 10-20 nm, a relevant length scale for next-generation devices. We study these materials by constructing nanoscale devices using electron-beam lithography and making measurements at low-temperatures.
Panel (A) showns a high-resolution transmission electron microscope image of a bismuth telluride nanowire synthesized by metal organic chemical vapor deposition. Bismuth telluride is a strongly layered compound, consisting of atomic sheets of bismuth and tellurium, arranged in groups of five. These 'quintuple layers' are visible as the banding within the wire. This particular wire is composed of 45 atomic layers.
The nanowires are atomically pristine and can be used a functional devices, as shown in (B). Electrical contacts, shown in yellow, are used to perform four-probe transport measurements on the nanowire, shown in red. Whereas imperfections are inevitably present in the “top-down” nanolithography which creates the electrical contacts, the “bottom-up” synthesis of the nanowire allow it to have atomic-level uniformity. In such measurements we have observed key signatures of phase coherent 1-D transport, including weak anti-localization.References
L. D. Alegria, J. R. Petta
Nanotech. 23, 435601 (2012)
L. D. Alegria, M. D. Schroer, A. Chatterjee, G. R. Poirier, M. Pretko, S. K. Patel, and J. R. Petta
Nano Lett. 12, 4711 (2012)