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

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.