Layer-by-layer entangled spin-orbital texture of the topological surface state in Bi₂Se₃

Z.-H. Zhu, C. N. Veenstra, G. Levy, A. Ubaldini, P. Syers, N. P. Butch, J. Paglione, M. W. Haverkort, I. S. Elfimov, and A. Damascelli

Accepted Monday Apr 22, 2013

We study Bi$_2$Se$_3$ by polarization-dependent angle-resolved photoemission spectroscopy (ARPES) and density-functional theory slab calculations. We find that the surface state Dirac fermions are characterized by a {\it layer-dependent} entangled spin-orbital texture, which becomes apparent through quantum interference effects. This explains the discrepancy between the spin polarization from spin-resolved ARPES -- ranging from 20 to 85\% -- and the 100\% value assumed in phenomenological models. It also suggests a way to probe the intrinsic spin texture of topological insulators, and to continuously manipulate the spin polarization of photoelectrons and photocurrents all the way from 0 to $\pm$100\% by an appropriate choice of photon energy, linear polarization, and angle of incidence.