Spin transport; quantum transport; new materials; topological insulators

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The main goal of this project is to explore the spin polarization of surface states in Bi-based topological insulators (TI) using an inverted device structure where the TI is electrically contacted from the bottom rather than from the top surface. This special fabrication method has the ability to significantly improve the TI-to-electrode interface yielding enhanced device performances. We suggest using two kinds of devices: (1) In the first set of devices we mechanically transfer a TI/hBN heterostructure onto Co/MgO and Au electrodes which were prepatterned on a Si++/SiO2 wafer. The ferromagnetic Co/MgO electrode acts as a spin-sensitive detector of the surface spin polarization which probes the spin accumulation at the TI-to-MgO/Co interface. Our devices offer to explore the TI surface spin polarization without disturbing fringe fields which may mask the measured spin voltages. (2) In the second set of devices, we aim to convert the surface spin polarization of the TI into a spin current which we inject from the TI surface into an adjacent graphene layer. This spin current shall be probed away from the TI material non-locally by spin-valve measurements using additional Co/MgO electrodes. In these devices, we expect to probe proximity-induced spin-orbit coupling at the TI-tographene interface. We also propose to use photo current measurements as spin sensitive probes of the TI surface polarization. While several previous photo current experiments only indirectly prove spin contributions by symmetry analysis of the measured polarization dependence, we aim to combine photo current excitation at the TI-to-graphene interface with spin-sensitive electrical read-out.