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arXiv · 1702.04176

Direct observation of the band gap transition in atomically thin ReS$_2$

Mathias Gehlmann·Irene Aguilera·Gustav Bihlmayer·Slavomír Nemšák·Philipp Nagler·Pika Gospodarič·Giovanni Zamborlini·Markus Eschbach·Vitaliy Feyer·Florian Kronast·Ewa Młyńczak·Tobias Korn·Lukasz Plucinski·Christian Schüller·Stefan Blügel·Claus M. Schneider
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Abstract

ReS$_2$ is considered as a promising candidate for novel electronic and sensor applications. The low crystal symmetry of the van der Waals compound ReS$_2$ leads to a highly anisotropic optical, vibrational, and transport behavior. However, the details of the electronic band structure of this fascinating material are still largely unexplored. We present a momentum-resolved study of the electronic structure of monolayer, bilayer, and bulk ReS$_2$ using k-space photoemission microscopy in combination with first-principles calculations. We demonstrate that the valence electrons in bulk ReS$_2$ are - contrary to assumptions in recent literature - significantly delocalized across the van der Waals gap. Furthermore, we directly observe the evolution of the valence band dispersion as a function of the number of layers, revealing a significantly increased effective electron mass in single-layer crystals. We also find that only bilayer ReS$_2$ has a direct band gap. Our results establish bilayer ReS$_2$ as a advantageous building block for two-dimensional devices and van der Waals heterostructures.

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Mathias Gehlmann, Irene Aguilera, Gustav Bihlmayer, Slavomír Nemšák, Philipp Nagler, Pika Gospodarič, Giovanni Zamborlini, Markus Eschbach, Vitaliy Feyer, Florian Kronast, Ewa Młyńczak, Tobias Korn, Lukasz Plucinski, Christian Schüller, Stefan Blügel, Claus M. Schneider. 2017-02-14. Direct observation of the band gap transition in atomically thin ReS$_2$. https://doi.org/10.1021/acs.nanolett.7b00627

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