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- ItemContrast 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
- ItemThe Weak 3D Topological Insulator Bi12Rh3Sn3I9(Weinheim : Wiley-VCH, 2020) Lê Anh, Mai; Kaiser, Martin; Ghimire, Madhav Prasad; Richter, Manuel; Koepernik, Klaus; Gruschwitz, Markus; Tegenkamp, Christoph; Doert, Thomas; Ruck, MichaelTopological insulators (TIs) gained high interest due to their protected electronic surface states that allow dissipation-free electron and information transport. In consequence, TIs are recommended as materials for spintronics and quantum computing. Yet, the number of well-characterized TIs is rather limited. To contribute to this field of research, we focused on new bismuth-based subiodides and recently succeeded in synthesizing a new compound Bi12Rh3Sn3I9, which is structurally closely related to Bi14Rh3I9 – a stable, layered material. In fact, Bi14Rh3I9 is the first experimentally supported weak 3D TI. Both structures are composed of well-defined intermetallic layers of ∞2[(Bi4Rh)3I]2+ with topologically protected electronic edge-states. The fundamental difference between Bi14Rh3I9 and Bi12Rh3Sn3I9 lies in the composition and the arrangement of the anionic spacer. While the intermetallic 2D TI layers in Bi14Rh3I9 are isolated by ∞1[Bi2I8]2− chains, the isoelectronic substitution of bismuth(III) with tin(II) leads to ∞2[Sn3I8]2− layers as anionic spacers. First transport experiments support the 2D character of this material class and revealed metallic conductivity. © 2020 The Authors. Published by Wiley-VCH GmbH
- ItemFreestanding Nanolayers of a Wide-Gap Topological Insulator through Liquid-Phase Exfoliation(Weinheim : Wiley-VCH, 2021) Lê Anh, Mai; Potapov, Pavel; Wolf, Daniel; Lubk, Axel; Glatz, Bernhard; Fery, Andreas; Doert, Thomas; Ruck, MichaelThe layered salt Bi14Rh3I9 is a weak three-dimensional (3D) topological insulator (TI), that is, a stack of two-dimensional (2D) TIs. It has a wide non-trivial band gap of 210 meV, which is generated by strong spin-orbit coupling, and possesses protected electronic edge-states. In the structure, charged layers of (Formula presented.) (Bi4Rh)3I]2+ honeycombs and (Formula presented.) Bi2I8]2− chains alternate. The non-trivial topology of Bi14Rh3I9 is an inherent property of the 2D intermetallic fragment. Here, the exfoliation of Bi14Rh3I9 was performed using two different chemical approaches: (a) through a reaction with n-butyllithium and poly(vinylpyrrolidone), (b) through a reaction with betaine in dimethylformamide at 55 °C. The former yielded few-layer sheets of the new compound Bi12Rh3I, while the latter led to crystalline sheets of Bi14Rh3I9 with a thickness down to 5 nm and edge-lengths up to several ten microns. X-ray diffraction and electron microscopy proved that the structure of Bi14Rh3I9 remained intact. Thus, it was assumed that the particles are still TIs. Dispersions of these flakes now allow for next steps towards the envisioned applications in nanoelectronics, such as the study of quantum coherence in deposited films, the combination with superconducting particles or films for the generation of Majorana fermions, or studies on their behavior under the influence of magnetic or electric fields or in contact with various materials occurring in devices. The method presented generally allows to exfoliate layers with high specific charges and thus the use of layered starting materials beyond van der Waals crystals. © 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH