Role of orbital angular momentum in the surface states of topological insulators

Changyoung Kim

 We performed angle resolved photoemission experiments with circularly polarized lights on topological insulators Bi2Se3. Strong circular dichroism signal is observed in the ARPES data from the surface states. The circular dichroism is attributed to the existence of chiral orbital angular momentum (OAM) in addition to the spin angular momentum (SAM). OAM is found to be anti-aligned with SAM to lower the energy stemming from the spin-orbital interaction Hamiltonian. First principles calculation also shows existence of the OAM with a very strong polarization. Our finding also implies that we can use circular dichroism ARPES to determine the spin direction in these materials. The method is further exploited to study the band warping effect on the angular momentum states in another topological insulator Bi2Te3. The angular momentum structure is found to be consistent with theoretical prediction as well as the experimental data from spin resolved photoemission. Implications of our findings will be also discussed.