Topological Surface States with Persistent High Spin Polarization across the Dirac Point inBi2Te2SeandBi2Se2

Helical spin textures with marked spin polarizations of topological surface states have been unveiled for the first time by state-of-the-art spin- and angle-resolved photoemission spectroscopy for two promising topological insulators, ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{2}\mathrm{Se}$ and ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{2}\mathrm{Te}$. Their highly spin-polarized natures are found to be persistent across the Dirac point in both compounds. This novel finding paves a pathway to extending the utilization of topological surface states of these compounds for future spintronic applications.