Non-local Fermi level tuning of topological insultor Bi_2-xSb_xSe₃nanoplate devices

The spin-polarized topological surface states of a topological insulators (TIs) are attractive because of their potential applications in spintronics. A critical challenge of accessing the surface states is to reliably tune the chemical potential with respect to the bulk bands and Dirac point. Here we report non-local Fermi level tuning in Bi_2-xSb_xSe₃ nanoplate devices. We found that applying a local electric field on a Bi_2-xSb_xSe₃ nanoplate device induces a Fermi level shift hundreds of microns away. As temperature decreases to 77K, such a Fermi level shift is frozen, and the device stay in a different electronic state. Magnitude and direction of the Fermi level shift can be controlled by the applied electric field, which then tune the device conductance, field effect behavior and photo-generated carrier transport distance. The non-local Fermi level shift follows very well with a diffusion model and predicts a diffusion coefficient of 2x10^-6cm²/S at room temperature. Potential candidates for the diffusing carriers include vacancies of selenium and charge traps.