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Author: Siemensmeyer, Konrad ×

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    Contrast Reversal in Scanning Tunneling Microscopy and Its Implications for the Topological Classification of SmB6
    (Weinheim : Wiley-VCH, 2020) Herrmann, Hannes; Hlawenka, Peter; Siemensmeyer, Konrad; Weschke, Eugen; Sánchez-Barriga, Jaime; Varykhalov, Andrei; Shitsevalova, Natalya Y.; Dukhnenko, Anatoliy V.; Filipov, Volodymyr B.; Gabáni, Slavomir; Flachbart, Karol; Rader, Oliver; Sterrer, Martin; Rienks, Emile D.L.
    SmB6 has recently attracted considerable interest as a candidate for the first strongly correlated topological insulator. Such materials promise entirely new properties such as correlation-enhanced bulk bandgaps or a Fermi surface from spin excitations. Whether SmB6 and its surface states are topological or trivial is still heavily disputed however, and a solution is hindered by major disagreement between angle-resolved photoemission (ARPES) and scanning tunneling microscopy (STM) results. Here, a combined ARPES and STM experiment is conducted. It is discovered that the STM contrast strongly depends on the bias voltage and reverses its sign beyond 1 V. It is shown that the understanding of this contrast reversal is the clue to resolving the discrepancy between ARPES and STM results. In particular, the scanning tunneling spectra reflect a low-energy electronic structure at the surface, which supports a trivial origin of the surface states and the surface metallicity of SmB6. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    A New Family of Layered Metal-Organic Semiconductors: Cu/V-Organophosphonates
    (Weinheim : Wiley-VCH, 2023) Tholen, Patrik; Wagner, Lukas; Ruthes, Jean G. A.; Siemensmeyer, Konrad; Beglau, Thi Hai Yen; Muth, Dominik; Zorlu, Yunus; Okutan, Mustafa; Goldschmidt, Jan Christoph; Janiak, Christoph; Presser, Volker; Yavuzçetin, Özgür; Yücesan, Gündoğ
    Herein, we report the design and synthesis of a layered redox-active, antiferromagnetic metal organic semiconductor crystals with the chemical formula [Cu(H2O)2V(µ-O)(PPA)2] (where PPA is phenylphosphonate). The crystal structure of [Cu(H2O)2V(µ-O)(PPA)2] shows that the metal phosphonate layers are separated by phenyl groups of the phenyl phosphonate linker. Tauc plotting of diffuse reflectance spectra indicates that [Cu(H2O)2V(µ-O)(PPA)2] has an indirect band gap of 2.19 eV. Photoluminescence (PL) spectra indicate a complex landscape of energy states with PL peaks at 1.8 and 2.2 eV. [Cu(H2O)2V(µ-O)(PPA)2] has estimated hybrid ionic and electronic conductivity values between 0.13 and 0.6 S m−1. Temperature-dependent magnetization measurements show that [Cu(H2O)2V(µ-O)(PPA)2] exhibits short range antiferromagnetic order between Cu(II) and V(IV) ions. [Cu(H2O)2V(µ-O)(PPA)2] is also photoluminescent with photoluminescence quantum yield of 0.02%. [Cu(H2O)2V(µ-O)(PPA)2] shows high electrochemical, and thermal stability.