Topological Insulators
The conducting surface states of a topological insulator can be altered to become insulating by inducing bulk ferromagnetism in the material via elemental doping. The figure shows the effects of Cr-doping on the magnetoconductivity in thin films of the topological insulator CrxBi2-xTe3 for x = 0 (a), x = 0.08 (b), x = 0.10 (c), and x = 0.14 (d). The pure Bi2Te3 film (a) exhibits weak anti-localization arising from the two-dimensional conducting surface states, indicated by the sharp downward cusp in the magnetoconductivity with the application of a small magnetic field. The film with x = 0.14 exhibits weak localization due to the increased disorder in the crystal from the Cr and is indicated by an upward cusp in magnetoconductivity at small magnetic fields (d). As the Cr concentration increases weak anti-localization can be seen to be suppressed due to the formation of a surface energy gap while weak localization becomes more dominant (b and c) due to the increased disorder in the crystal.
Project participants: Nick Meyer, Michelle Yan Ni, Ikenna Nlebedim, David Jiles