Dresden 2026 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 38: Topology and symmetry protected materials & Topological insulators – Poster (joint session O/TT)

TT 38.4: Poster

Tuesday, March 10, 2026, 14:00–16:00, P2

The quasi one-dimensional van der Waals material α-Bi₄Br₄ — •Jonathan K. Hofmann^1,2, Serhii Kovalchuk^1,3, Mingqian Zheng⁴, Yuqi Zhang⁴, Vasily Cherepanov¹, Timofey Balashov¹, Jin-Jian Zhou⁴, Zhiwei Wang⁴, Yugui Yao⁴, Irek Morawski³, F. Stefan Tautz^1,2, Felix Lüpke^1,5, and Bert Voigtländer^1,2 — ¹Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, Germany — ²Experimentalphysik IV A, RWTH Aachen University, Germany — ³Institute of Experimental Physics, University of Wrocław, Poland — ⁴Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement, Beijing Institute of Technology, China — ⁵II. Physikalisches Institut, Universität zu Köln, Germany

α-Bi₄Br₄ is a quasi-one-dimensional material: covalently bonded Bi₄Br₄ chains are arranged in parallel, side-by-side and layer-by-layer, with van der Waals gaps in between. Bulk α-Bi₄Br₄ is higher-order topological insulator. At step edges on the (001) surface, quantum spin Hall (QSH) edge states are present. Using a scanning tunneling microscope (STM), we observe a significant shift of the chains, relative to each other, which we attribute to shear stress. Scanning tunneling spectroscopy reveals that the edge states are robust against the strain. Density functional theory confirms that a strained monolayer of Bi₄Br₄ is a QSH insulator with Z₂=1. Furthermore, we use a four-tip STM to analyze the electrical transport of α-Bi₄Br₄ in situ.

Keywords: Scanning Tunneling Microscope; Higher-order Topological Insulator; Shear stress; four-tip Scanning Tunneling Microscope; quasi-one-dimensional crystal