Current induced spin polarization in 3D topological insulator thin films

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This project aims to experimentally demonstrate current-induced spin polarization within the surface states of three-dimensional topological insulator thin films. The required spin detection capability shall be implemented with the aid of a ferromagnetic metal contact, which is separated from the topological insulator by a thin layer of graphene serving as a tunnel barrier that ensures suitable spin-impedance matching conditions. In addition, the graphene is devised to chemically stabilize the interface, thus enabling to preserve the spin information of the crossing carriers. Two different strategies are envisioned in order to avoid cancelation of the spin polarization due to the opposite chiralities of the carriers on the opposite surfaces. In the first approach, it is planned to open an energy gap in one of the surfaces by coating it with an ultrathin magnetic film. The second strategy involves the implementation of a back and top gate that enable tuning the two surfaces independently into the nand p-type regime, respectively. For the latter task, antimony-doped TI nanosheets (BixSb1-x)2Te3 exhibiting a strongly suppressed bulk electron concentration shall be prepared by a vapor-solid growth method. Detailed studies of the magnetic field-dependent switching behavior of the devices as a function of temperature, the thickness of the graphene layer, as well as the gate-controlled carrier concentration shall provide valuable information regarding the spin generating capability of topological insulators.