Regensburg 2019 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 80: Ultrafast Electron Dynamics at Surfaces and Interfaces I
O 80.2: Vortrag
Donnerstag, 4. April 2019, 10:45–11:00, H16
Practical Limitations of Floquet Topological Insulators — •Sven Aeschlimann1, Mariana Chavez-Cervantes1, Razvan Krause1, Camilla Coletti2, Kai Roßnagel3, and Isabella Gierz1 — 1Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, Hamburg, Germany — 2Center for Nanotechnology @ NEST, Istituto Italiano di Tecnologia, Pisa, Italy — 3Institute of Experimental and Applied Physics, Christian-Albrechts-Universität zu Kiel, Kiel, Germany
Recently, using Floquet theory, Oka and Aoki [1] realized that graphene illuminated by circularly polarized light provides and experimental realization of the Haldane model [2] that predicts the occurrence of a quantum Hall effect in the absence of magnetic fields. We used time-and angle-resolved photoemission spectroscopy to search for the predicted Floquet sidebands, changes of the photoemission matrix element due to the induced non-zero z-component of the pseudospin, and band gap opening [3]. After careful optimization of all experimental parameters we observed Floquet sidebands in cleaved bulk WSe2 crystals but not in epitaxial graphene. We attribute the absence of Floquet effects in graphene to scattering times that are short compared to the period of the driving field. Our results have important implications for the experimental realization of Floquet topological insulators and related proposals [4].
[1] T. Oka and H. Aoki, PRB 79, 081406 (2009) [2] F. D. M. Haldane, Phys. Rev. Lett. 61, 2015 (1988) [3] M. A. Sentef et al., Nat. Commun. 6, 7047 (2015) [4] M. Claassen et al., Nat. Commun. 7, 13074 (2016)