light and first-principles density functional calculation with spin-orbit coupling to study
surface states of a topological insulator Bi 2 Se 3. We observed circular dichroism (CD) as
large as 30% in the ARPES data with upper and lower Dirac cones showing opposite signs
in CD. The observed CD is attributed to the existence of local orbital-angular momentum
(OAM). First-principles calculation shows that OAM in the surface states is significant and is …