Observation of Time-Reversal-Protected Single-Dirac-Cone Topological-Insulator States in Bi 2 Te 3 and Sb 2 Te 3

We show that the strongly spin-orbit coupled materials ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ and ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ and their derivatives belong to the ${Z}_{2}$ topological-insulator class. Using a combination of first-principles theoretical calculations and photoemission spectroscopy, we directly show that ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ is a large spin-orbit-induced indirect bulk band gap ($\ensuremath{\delta}\ensuremath{\sim}150\text{ }\text{ }\mathrm{meV}$) semiconductor whose surface is characterized by a single topological spin-Dirac cone. The electronic structure of self-doped ${\mathrm{Sb}}_{2}{\mathrm{Te}}_{3}$ exhibits similar ${Z}_{2}$ topological properties. We demonstrate…