A combined theoretical and experimental study reveals evidence for the dual topological insulating character of the stoichiometric natural superlattice phase Bi1Te1=[Bi2]1[Bi2Te3]2, being a stack of alternating Bi bilayers and two quintuple layers of Bi2Te3. We identify Bi1Te1 by density functional theory to exhibit a non trivial time-reversal symmetry-driven character of Z2=(0;001) and additionally a mirror-symmetry induced mirror Chern number of nM=−2, which indicates that Bi1Te1 is both a weak topological insulator and a topological crystalline insulator. The coexistence of the two phenomena preordains distinct crystal planes to host topological surface states that are protected by the respective symmetries. The surface perpendicular to the stacking direction is the 'dark' surface of the weak topological insulator, while hosting mirror-symmetry protected surface states along the ΓMˉ direction at non-time-reversal invariant momenta points. We confirm the stacking sequence of our MBE-grown Bi1Te1 thin films by X-ray diffraction and transmission electron microscopy, and find indications of the topological crystalline and weak topological character in the surface electronic spin structure by spin- and angle-resolved photoemission spectroscopy, which nicely match the results from density functional theory.
@article{arxiv.1604.08886,
title = {$\mbox{Bi}_{1}\mbox{Te}_{1}$: a dual topological insulator},
author = {Markus Eschbach and Martin Lanius and Chengwang Niu and Ewa Młyńczak and Pika Gospodarič and Jens Kellner and Peter Schüffelgen and Mathias Gehlmann and Sven Döring and Elmar Neumann and Martina Luysberg and Gregor Mussler and Lukasz Plucinski and Markus Morgenstern and Detlev Grützmacher and Gustav Bihlmayer and Stefan Blügel and Claus M. Schneider},
journal= {arXiv preprint arXiv:1604.08886},
year = {2017}
}