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Theme 3 colloquium: "How Robust are Topological States?" (Lecture)

Tuesday 17 October 2017Add to my calendar
from 16:00
prof. Matthias Bode

Topological insulators (TIs) have recently attracted considerable interest because they host linearly dispersing surface states that are strongly spin-orbit–coupled such that spin and electron momentum are tightly locked, thereby resulting in charge currents which are intrinsically tied to the spin. This property makes TIs promising candidates for spintronics applications.
In this talk I will describe how TIs respond to magnetic dopants that are deposited onto the surface [1,2] or into the bulk [3]. In particular, I will discuss various electronic scattering channels, which can be mapped by the so-called quasiparticle interference (QPI) method. In combination with local tunneling spectroscopy it allows for an extremely precise understanding of how topological states respond to magnetic impurities at the atomic scale. The combination of real and reciprocal space techniques elucidates a delicate balance between two opposite trends, that is, gap opening and the emergence of a Dirac node impurity bands, both induced by the magnetic dopants [3]. Finally, I will report on the discovery of a new type of one-dimensional (1D) electronic states which exist at step edges of the topological crystalline insulator (TCI) Pb1-xSnxSe [4]. They form conductive channels which are only 10 nanometers wide and exhibit a surprising robustness against external perturbations.

(Top) Schematic representation of the fig coll Matthias Bode okt2017atomic arrangement at double (left) and single (right) step edges on topological crystalline insulators with rock salt structure. The differently colored rectangles indicate the preservation and breaking of translational symmetry, respectively. (Bottom) conductance map measured with a scanning tunneling microscope showing a strongly enhanced signal at the single step edge.

[1] P. Sessi et al., Nature Comm. 5, 5349 (2014)
[2] T. Bathon et al., Nano Lett. 15, 2442 (2015)
[3] P. Sessi et al., Nature Comm. 7, 12027 (2016)
[4] P. Sessi et al., Science 354, 1269 (2016)