| AVS 63rd International Symposium & Exhibition | |
| Magnetic Interfaces and Nanostructures | Monday Sessions |
| Session MI+2D+AC-MoA |
| Session: | Magnetism and Spin Orbit Effects at Interfaces and Surfaces: Recent Experimental and Theoretical Advances |
| Presenter: | Peter Krüger, Westfälische Wilhelms-Universität Münster, Germany |
| Authors: | P. Krüger, Westfälische Wilhelms-Universität Münster, Germany T. Förster, Westfälische Wilhelms-Universität Münster, Germany M. Rohlfing, Westfälische Wilhelms-Universität Münster, Germany P. Eickholt, Westfälische Wilhelms-Universität Münster, Germany A.B. Schmidt, Westfälische Wilhelms-Universität Münster, Germany M. Donath, Westfälische Wilhelms-Universität Münster, Germany |
| Correspondent: | Click to Email |
The generation of spin-polarized electrons on the basis of spin-orbit coupling at the surfaces of nonmagnetic solids has attracted considerable interest in recent years. Adlayers of heavy atoms, in particular, give rise to an interesting physics of spin-split surface states going far beyond the simple Rashba model. However, only very few studies have been reported that address unoccupied states of these systems, despite their relevance for potential applications. In the first part of this contribution, we present results from ab-initio calculations as well as spin- and angle-resolved inverse photoemission (IPE) for systems showing empty bands with a giant spin splitting and a unique structure of the spin polarization. For Tl/Si(111) and Tl/Ge(111), we identify spin-split states whose polarization vector rotates from the Rashba direction to an out-of-plane polarization when going from Gamma to K. Surprisingly, the spin splitting of the bands on Tl/Ge(111) is much smaller than on Tl/Si(111) despite the stronger surface localization and the heavier substrate. Our detailed analysis of the electronic structure shows that a remarkable interplay between spin-orbit coupling and hybridization is responsible for this unexpected result. Furthermore, we notice a distinct spin asymmetry in the intensity of the measured spectra at M, a time-invariant k-point. Our simulations of the IPE process unravel this puzzling behavior.
In the case of topological insulators, spin-orbit coupling gives rise to topologically protected surface states. We identify problems of the widely used density-functional theory (DFT) with a proper description of these states and demonstrate that they can be overcome by employing the GW self-energy operator within ab initio many-body perturbation theory. In particular we have investigated thin films of Bi2Se3, Bi2Te3, and Sb2Te3 with thicknesses from one to six quintuple layers. The quasiparticle band structures show highly improved agreement with experiments compared to DFT. In addition to a correction of the band gaps, the energetic positions and dispersions of the surface states change significantly around the Dirac point. As the wave functions are updated in our approach, the two-dimensional topological phases (quantum spin Hall or trivial) in GW can be different from the DFT result. We find the nontrivial quantum spin Hall phase, together with a sizable band gap 0.13 eV for a Bi2Te3 slab of 2 QL thickness.
[1] P. Eickholt et al., Phys. Rev. B 93, 085412 (2016)
[2] T. Förster et al., Phy. Rev. B 92, 291404 (R) (2015)