Controlling Spin-Polarized Currents on the Surface of Topological Insulators*

The appearance of topologically protected spin-momentum locked surface states with forbidden backward scattering on the surface of topological insulators gives rise to robust room temperature spin currents making them ideal candidates for the realization of spintronic devices. So far however, despite a decade of research in this field, very little is known on how to access and manipulate such currents in a manner that is accessible in chip-based devices. Here we reveal a technique to generate long-lived spin-currents of arbitrary geometry with tunable magnitude and duration on the surface of Bi₂Se₃ topological insulators. Time-resolved angle-resolved photoemission spectroscopy, together with a quantitative model, uncovers a remarkable contrast with respect to doping thanks to the intrinsic correlation between the spin-locked surface state and an insulating bulk. This work demonstrates that localized spin-currents are accessible with long lifetimes, easily tuned in both magnitude and duration, merging photonics and spintronics based devices on the same material.