Figure 1
Illustration: Reproduced from [5]

Figure 1: The energy vs momentum of the states on the surface of a 3D topological insulator forms a Dirac cone. The red curve is a slice through this cone, measured with photoemission from the surface of the topological insulator Bi2Se3. (Inset) Schematic of the full Dirac cone and the circulation of the spin states (yellow arrows) associated with each momentum state. The spin circulation pattern leads to a Berry’s phase of π.