Photon energy dependence of circular dichroism in angle-resolved photoemission spectroscopy of Bi 2 Se 3 Dirac states

Circular dichroism in angle-resolved photoemission spectroscopy (CD-ARPES) has been recently proposed as a sensitive probe of either the spin texture or the orbital momentum texture of helical Dirac fermions at the surface of three-dimensional topological insulators. Recent results obtained on Bi2Te3 point rather towards a final state effect. In this Rapid Communication, we study the prototypical topological insulator Bi2Se3 by CD-ARPES as a function of the photon energy and as a function of thickness. Analysis of the photon energy dependence of CD-ARPES, as well as the existence of a large dichroic signal from massive Dirac fermion states in ulthathin films, confirm that the dichroism is predominantly a final state effect. © 2013 American Physical Society.