Figure 1
Illustration: top Carin Cain; bottom from Ref. [8]

Figure 1: (Top) Idealized surface dispersion for doped topological insulator CuxBi2Se3. Shaded area corresponds to occupied bulk modes. Linearly dispersing surface modes meet at the time-reversal invariant momentum k=0. (Bottom) Crystal structure of CuxBi2Se3, showing intercalated copper layers.