Spin-to-Charge Conversion Manipulated by Fine-Tuning the Fermi Level of Topological Insulator (Bi_1–xSb_x)₂Te₃

The efficiency of spin-to-charge conversion is a key parameter in determining the performance of emerging spintronic devices. In the topological surface state of a topological insulator (TI), the spin-momentum locking effect offers a great possibility for efficient spin-to-charge conversion. Here, we report the relation between the Fermi level position EF and spin-to-charge conversion efficiency in heterostructure Ni80Fe20 (Py)/(Bi1–xSbx)2Te3. The band structure of (Bi1–xSbx)2Te3 films becomes tailored by tuning the ratio of bismuth to antimony so that the position of the Fermi level EF varies from the top side of the valence band to the bottom side of the conduction band through the in-gap surface Dirac cone. The result is consistent with the electronic behavior of the majority carriers varying from n-type to p-type. In spin-pumping measurements, we observed that the inverse Edelstein effect length (λIEE) with a tuned EF near the Dirac point is significantly enhanced, indicating that the spin-charge conversion is determined mainly by the topological surface state. These results demonstrate that fine-tuning of EF in a TI-based heterostructure is critical to maximizing the efficiency of spin-to-charge conversion using a spin-momentum locking mechanism.