Phys. Rev. Lett. 113, 196601 (2014)

Magnetization precession in a ferromagnet can be used to inject spin currents into a range of materials — an effect known as spin pumping. When spins are injected into a material with a large spin–orbit coupling, the inverse spin Hall effect, which causes spins with opposite signs to scatter in opposing directions, converts the spin current into a charge current. This combination of spin pumping and the inverse spin Hall effect is commonly used in spintronic devices. Yuki Shiomi and colleagues have now demonstrated a different type of spin-to-charge conversion using the surface states of a topological insulator.

The conductive topologically protected surface states of topological insulators exhibit a locking between the spin and momentum, so the spin direction determines the electron motion, and vice versa. Shiomi et al. used this spin-momentum locking to convert a pumping-induced spin current into a charge current. Although similar to the conversion reported in materials with a large Rashba coupling, much higher efficiencies should be possible with topological surface states, offering an alternative method for efficient spin-to-charge conversion.