SFB Extra Seminar

In the recent years topological materials have attracted a lot of research interest, which lead to the discovery of a plethora of radically new materials. Topological matter such as topological insulators (TIs) host great potential for future technology ranging from low-power electronics to possible quantum information devices. One of the most prominent examples of the exciting new physics that is found in these materials is the long-sought for quantum anomalous Hall effect (QAH) which was predicted and first discovered in magnetically doped topological insulators [1,2].

However, the quest for QAH materials to date only succeeded for systems which have very low critical temperatures. This calls for a better understanding of these materials and finally improved control over the magnetic state in magnetic TIs.

Based on a combination of ab-initio calculations and x-ray magnetic circular dichroism and resonant photoemission spectroscopy, we investigate the magnetic exchange coupling mechanism in the transition metal-doped topological insulators Bi2Te3 and Sb2Te3 [3,4]. We are able to demonstrate the competing nature of different exchange coupling mechanisms that favor either ferro- or antiferromagnetic interactions among the magnetic dopants embedded into TIs. Furthermore, we are able to show how the magnetic exchange interactions can be tuned making use of their distance dependence and spatial directionality as well as their susceptibility to changes in the position of the Fermi level throughout the gap region of the TI host materials. This will eventually enable us to have a fine control over the magnetic state by varying the spatial distribution of magnetic atoms in the TI host materials and via additional Fermi level engineering in the TI host material.

In this contribution, I will focus on the ab-initio calculations of our combined theoretical and experimental investigations [3,4] and highlight the underlying mechanisms of the exchange interaction. Our calculations are performed within the framework of density functional theory using the relativistic Korringa-Kohn-Rostoker Green function method [5]. To model doping with magnetic transition metal atoms into the TI materials, we make use of the Dyson equation that allow us to efficiently embed impurities fully ab-initio into the host crystals.

[1] R. Yu, et al., Science 329, 5987 (2010). doi:10.1126/science.1187485
[2] C.-Z. Chang et al., Science 340, 6129 (2013). doi:10.1126/science.1234414
[3] P. Rüßmann et al., J. Phys. Mater. 1, 015002 (2018)
[4] T. R. F. Peixoto, H. Bentmann, P. Rüßmann et al., in preparation (2019)
[5] https://jukkr.fz-juelich.de