Electrical Detection of the Spin Polarization Due to Charge Flow in the Surface State of the Topological Insulator Bi₁.₅Sb₀.₅Te₁.₇Se₁.₃

We detected the spin polarization due to charge flow in the spin nondegenerate surface state of a three-dimensional topological insulator by means of an all-electrical method. The charge current in the bulk-insulating topological insulator Bi₁.₅Sb₀.₅Te₁.₇Se₁.₃ (BSTS) was injected/extracted through a ferromagnetic electrode made of Ni₈₀Fe₂₀, and an unusual current-direction-dependent magnetoresistance gave evidence for the appearance of spin polarization, which leads to a spin-dependent resistance at the BSTS/Ni₈₀Fe₂₀ interface. In contrast, our control experiment on Bi₂Se₃ gave null result. These observations demonstrate the importance of the Fermi-level control for the electrical detection of the spin polarization in topological insulators.