Regensburg 2016 – scientific programme

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O: Fachverband Oberflächenphysik

O 63: Scanning Probe Microscopy and Spin Phenomena

O 63.1: Invited Talk

Wednesday, March 9, 2016, 15:00–15:30, H4

Spin-orbit coupling, magnetic perturbations, and competing trends in topological insulators — •Matthias Bode — Physikalisches Institut, Experimentelle Physik II, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany

Topological insulators (TIs) interacting with magnetic perturbations lead to several unconventional effects, usually described within the framework of gapping the Dirac quasiparticles due to broken time-reversal symmetry [1,2]. While the quantum anomalous Hall effect confirmes the presence of ferromagnetically gapped Dirac states, the overwhelming majority of photoemission and tunneling data demonstrate the presence of a finite density of states at the Dirac point even once the system becomes magnetic. We present a series of experiments which, by mapping the response of TIs to different magnetic impurities down to the atomic level, provide a detailed microscopic picture and thereby solve these contradictory observations in both surface- and bulk-doped samples. We provide evidence of highly anisotropic Dirac fermion-meditated magnetic interactions that lead to quantum coherent states propagating over mesoscopic distances. We also show that magnetic order and gapless states can coexist due to the emergence of a two-fluid behavior where the competition in between opposite trends, i.e. gap-opening vs. gap-closing, is ultimately linked to the localized vs. delocalized nature of the perturbations-induced quasiparticles.

[1] P. Sessi et al., Phys. Rev. B 88, 161407 (2013).

[2] P. Sessi et al., Nature Comm. 5, 5349 (2014).