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arXiv · 2403.14560

Moiré-modulated band gap and van Hove singularities in twisted bilayer germanene

Pantelis Bampoulis·Carolien Castenmiller·Dennis J. Klaassen·Jelle v. Mil·Paul L. de Boeij·Motohiko Ezawa·Harold J. W. Zandvliet
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Abstract

Twisting bilayers of two-dimensional topological insulators has the potential to create unique quantum states of matter. Here, we successfully synthesized a twisted bilayer of germanene on Ge2Pt(101) with a 21.8$^o$ degrees twist angle, corresponding to a commensurate ($\sqrt{7} \times \sqrt{7}$) structure. Using scanning tunneling microscopy and spectroscopy, we unraveled the structural and electronic properties of this configuration, revealing a moiré-modulated band gap and a well-defined edge state. This band gap opens at AB/BA stacked sites and closes at AA stacked sites, a phenomenon attributed to the electric field induced by the scanning tunneling microscopy tip. Our study further revealed two van Hove singularities at -0.8 eV and +1.04 eV, resulting in a Fermi velocity of $(8 \pm 1) \times 10^5$ m/s. Our tight-binding results uncover a unique quantum state, where the topological properties could be regulated through an electric field, potentially triggering two topological phase transitions.

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Pantelis Bampoulis, Carolien Castenmiller, Dennis J. Klaassen, Jelle v. Mil, Paul L. de Boeij, Motohiko Ezawa, Harold J. W. Zandvliet. 2024-03-21. Moiré-modulated band gap and van Hove singularities in twisted bilayer germanene. https://doi.org/10.1088/2053-1583%2Fad4166

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