Seminars Archive

Robust quantum spin Hall and quantum anomalous Hall phases from first principles

Abstract
The realization of dissipationless spin- and charge transport in two-dimensional (2D) topological insulators (TIs) requires the optimization of material parameters, e.g., the stabilization of the 2D material on a substrate maintaining a suitable size and position of the band-gap, a reasonable localization of the edge states or, for the Chern insulators, the introduction of a proper exchange splitting in the material. Density functional theory is a powerful tool to predict these properties and give new ideas to design functional materials experimentally. In this contribution, the focus will be on functionalized variants of Bi bilayers, but also 2D TIs that are obtained as thin films of their three-dimensional counterparts. While contact with substrates often leads to doping that shifts the band-gap away from the Fermi level [1], hydrogenation can minimize the interactions so that a Bi layer can be stabilized on a MoS2 substrate maintaining its insulating properties [2]. The functionalization also allows to introduce magnetism in the layer and to realize the so-called valley-polarized quantum anomalous Hall effect. This will be compared to other strategies proposed to drive a system from the quantum spin Hall to the quantum anomalous Hall regime, e.g., by proximity of a magnetic substrate [3]. Finally, the prospects of 2D topological crystalline insulators and their practical realization will be shortly discussed. This work was supported by the Priority Program 1666 of the German Research Foundation and the Virtual Institute for Topological Insulators of the Helmholtz Association. References 1. T. Hirahara, G. Bihlmayer, Y. Sakamoto, M. Yamada, H. Miyazaki, S-i. Kimura, S. Blügel, and S. Hasegawa, Phys. Rev. Lett. 107, 166801 (2011), A. Eich, M. Michiardi, G. Bihlmayer, X.-G. Zhu, J.-L. Mi, Bo B. Iversen, R. Wiesendanger, Ph. Hofmann, A. A. Khajetoorians, and J. Wiebe , Phys. Rev. B 90, 155414 (2014) 2. C. Niu, G. Bihlmayer, H. Zhang, D. Wortmann, S. Blügel, and Y. Mokrousov, Phys. Rev. B 91, 041303 (2015) 3. H. Zhang, F. Freimuth, G. Bihlmayer, S. Blügel, and Y. Mokrousov, Phys. Rev. B 86, 035104 (2012)