Ab initio description of quasiparicle spin interference and time-reversal scattering processes off magnetic impurties

In structure inversion-asymmetric environments such as surfaces and interfaces the spin of quasiparticles can have a profound effect on their interference. Quasiparticle interference patterns measured typically by scanning tunneling microscopy are not related in a trivial way to the dispersion of the electronic states. In fact, for Bi(110) [1] we could show that the observed interference patterns can be interpreted only by taking spin-conserving scattering events into account. In this contribution we go one step further and include explicitly in the analysis the scattering of single non-magnetic and magnetic impurities with and without spin-orbit interaction. We present density-functional calculations of the quasiparticle interference at surfaces due to scattering off magnetic adatoms. We consider two substrates Au(111) and a thin film of Bi2Te3, a three-dimensional topological insulator (3D-TI). Our focus is on 3d impurities on Au(111) where the spin-orbit coupling (SOC) causes a Rashba-type splitting of the surface. The spin polarization of the quasiparticle waves shows a non-collinear behavior because of SOC. We compare to previous model-based results [2] and discuss the relation to the scattering properties of the impurity. As a matter of principle, magnetic impurities at surfaces break the topological protection in 3D-TI and we study this loss of protection by taking into account time-reversed transitions caused by the magnetic moment. In our calculations we employ the KKR-Green function method for the electronic structure and scattering properties at defects [3, 4]. We acknowledge financial support from the DFG (SPP-1666) and from the VITI project (DBB01126) of the Helmholtz Association and computational support from the JARA-HPC Supercomputing Centre at the RWTH Aachen University. [1] J.I. Pascual, G. Bihlmayer, Yu. M. Koroteev, H.-P. Rust, G. Ceballos, M. Hansmann, K. Horn, E. V. Chulkov, S. Blügel, P. M. Echenique, and Ph. Hofmann Phys. Rev. Lett. 93, 196802 (2004)[2] S. Lounis, A. Bringer, and S. Blügel, Phys. Rev. Lett. 108, 207202 (2012).[3] S. Heers, PhD Thesis, RWTH Aachen (2011); D.S.G. Bauer, PhD Thesis, RWTH Aachen (2013), B. Zimmerman, PhD Thesis, RWTH Aachen (2014)[4] N. H. Long, P. Mavropoulos, B. Zimmermann, D. S. G. Bauer, S. Blügel, and Y. Mokrousov, Phys. Rev. B 90, 064406 (2014