Oscillatory surface dichroism of the insulating topological insulator Bi2Te2Se

Using circular dichroism-angle resolved photoemission spectroscopy, we report a study of the effect of angular momentum transfer between polarized photons and topological surface states on the surface of the insulating topological insulator Bi2Te2Se. The photoelectron dichroism is found to be strongly modulated by the frequency of the helical photons including a dramatic sign flip. Our results suggest that the observed dichroism and its sign flip are consequences of strong coupling between the photon field and the spin-orbit nature of the Dirac modes on the surface. Our studies reveal the intrinsic dichroic behavior of topological surface states and point toward the potential utility of bulk insulating topological insulators in opto-spintronics device applications.