Photoelectron spin-flipping and texture manipulation in a topological insulator

A hallmark characteristic of the recently discovered topological insulators is their protected metallic surface states. Electrons in these surface states are spin polarized with their spins governed by their momentum, resulting in a helical spin texture in momentum space. Spin- and angle-resolved photoemission spectroscopy has been the only tool capable of directly observing this central feature with simultaneous energy, momentum, and spin sensitivity. By using an innovative photoelectron spectrometer with a high-flux laser, we found that the spin polarization of the resulting photoelectrons exhibits rich phenomena previously unobserved. These surprising results provide insight into the physics of these fascinating materials and the use of spin-resolved photoemission in general.