Spin-polarized surface bands of a three-dimensional topological insulator studied by high-resolution spin- And angle-resolved photoemission spectroscopy

Abstract

The spin-polarized surface band structure of the three-dimensional (3D) quantum spin Hall phase of Bi1-x Sbx (x = 0.12-0.13) was studied by spinand angle-resolved photoemission spectroscopy (SARPES) using a high-yield spin Polarimeter equipped with a high-resolution electron spectrometer. The spin-integrated spectra were also measured and compared to those of Bi1-x Sbx with x = 0.04. Band dispersions of the edge states were fully elucidated between the two time-reversal-invariant points, Γ̄ and M̄, of the (111) surface Brillouin zone. The observed spin-polarized band dispersions at x = 0.12-0.13 indicate an odd number of the band crossing at the Fermi energy, giving unambiguous evidence that this system is a 3D strong topological insulator, and determine the 'mirror chirality' to be -1, which excludes the existence of a Dirac point in the middle of the Γ̄-M̄ line. The present research demonstrates that the SARPES measurement with energy resolution ≤ 50 meV is one of the critical techniques for complementing the topological band theory for spins and spin currents. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.