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arXiv · 2101.01140

A full gap above the Fermi level: the charge density wave of monolayer VS2

Camiel van Efferen·Jan Berges·Joshua Hall·Erik van Loon·Stefan Kraus·Arne Schobert·Tobias Wekking·Felix Huttmann·Eline Plaar·Nico Rothenbach·Katharina Ollefs·Lucas Machado Arruda·Nick Brookes·Gunnar Schoenhoff·Kurt Kummer·Heiko Wende·Tim Wehling·Thomas Michely
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Abstract

In the standard model of charge density wave (CDW) transitions, the displacement along a single phonon mode lowers the total electronic energy by creating a gap at the Fermi level, making the CDW a metal--insulator transition. Here, using scanning tunneling microscopy and spectroscopy and ab initio calculations, we show that VS$_2$ realizes a CDW which stands out of this standard model. There is a full CDW gap residing in the unoccupied states of monolayer VS$_2$. At the Fermi level, the CDW induces a topological metal-metal (Lifshitz) transition. Non-linear coupling of transverse and longitudinal phonons is essential for the formation of the CDW and the full gap above the Fermi level. Additionally, x-ray magnetic circular dichroism reveals the absence of net magnetization in this phase, pointing to coexisting charge and spin density waves in the ground state.

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Camiel van Efferen, Jan Berges, Joshua Hall, Erik van Loon, Stefan Kraus, Arne Schobert, Tobias Wekking, Felix Huttmann, Eline Plaar, Nico Rothenbach, Katharina Ollefs, Lucas Machado Arruda, Nick Brookes, Gunnar Schoenhoff, Kurt Kummer, Heiko Wende, Tim Wehling, Thomas Michely. 2021-01-04. A full gap above the Fermi level: the charge density wave of monolayer VS2. https://doi.org/10.1038/s41467-021-27094-x

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