Photocurrent measurements in topological insulator Bi2Se3 nanowires

Circular photogalvanic currents are a promising approach for spin-optoelectronics. To date, such currents have been induced in topological insulator flakes or extended films. It is not clear whether they can be generated in nanodevices. In this paper, we demonstrate the generation of circular photogalvanic currents in Bi2Se3 nanowires. Each nanowire shows topological surface states. Here, we generate and distinguish the different photocurrent contributions via the driving light wave. We separate the circular photogalvanic currents from those due to thermal Seebeck effects through controlling laser light polarization. The results reveal a spin-polarized surface-Dirac electron flow in the nanowires arising from spin-momentum locking and spin–orbit effects. The second photocurrent contribution described in this Letter is caused by the thermal Seebeck effect. By scanning the photocurrent, it can be spatially resolved; upon reversing the gradient direction along the nanowire, the photocurrent changes its sign, and close to the gold contacts, the amplitudes of the different photocurrent contributions are affected by the proximity to the contacts. In the center of the nanowires, where the effects from the gold contact/topological insulator stacks vanish, the spin-polarized current remains constant along the nanowires. This allows the all-optical spin current generation in topological insulator nanowires and hybrid structures on the nanoscale, one goal of spin-orbitronics.