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Diagram of the proposed scheme to inject a spin polarized current into a topological insulator. A tunnel junction injects unpolarized hot electrons from a NM metal cathode into a FM anode. After attenuation of minority spin electrons, electrons enter the Si conduction band accelerated by a voltage V c 1 and enter the Bi 2 Se 3 with excess energy given by the Bi 2 Se 3 -Si Schottky barrier height. Spin-momentum conversion in Bi 2 Se 3 leads to a spin dependent difference in currents I1 and I2. The direction of injected spin is controlled by precession in the applied magnetic field during the Si transport time (). Inset: schematic of band structure of Si and Bi 2 Se 3 showing spin polarized surface states (SS) and unpolarized bulk conduction (BCB) and valence (BVB) bands of Bi 2 Se 3 .
Transport measurements of two of the Bi 2 Se 3 crystals studied. (a) Optical image of Bi 2 Se 3 samples showing Cr/Au electrodes and HSQ isolation layer to prevent direct contact between Cr/Au electrodes and Si. (b) Linear four probe and two probe I-V characteristics of samples 1 and 2, respectively. (In sample 1, current was driven through electrodes 1 and 4 and voltage was measured in electrodes 2 and 3). (c) Two probe resistance of samples 1 and 2 as a function of temperature.
(a) and (b) Current I through the In-silicon-Bi 2 Se 3 -Cr/Au structure as a function of measured between In and Cr/Au and a second contact on the Bi 2 Se 3 shown in (b). (c) shows a schematic of the measurement setup. Measurements at different temperatures T are shown as indicated by legend in (a). (c) Semi-log plot of as a function of 1/T for Si-Bi 2 Se 3 junctions samples 1 and 2. Straight lines are fits to the Richardson-Dushman thermionic emission theory (Eq. (1)) with a Schottky barrier height of 0.34 eV.
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