4.8 Article

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

Journal

NATURE COMMUNICATIONS
Volume 12, Issue 1, Pages -

Publisher

NATURE PORTFOLIO
DOI: 10.1038/s41467-021-27094-x

Keywords

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Funding

  1. Deutsche Forschungsgemeinschaft (DFG, German Research foundation) [CRC 1238, 277146847]
  2. DFG [EXC 2077, GRK 2247, SPP 2244]
  3. European Graphene Flagship [881603]
  4. Central Research Development Fund of the University of Bremen
  5. CAPES [9469/13-3]

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In monolayer VS2, a CDW gap resides in the unoccupied states but induces a topological metal-metal transition at the Fermi level. Additionally, the non-linear coupling of transverse and longitudinal phonons is essential for the formation of the CDW.
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 VS2 realizes a CDW which stands out of this standard model. There is a full CDW gap residing in the unoccupied states of monolayer VS2. 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. A charge density wave (CDW) normally creates a gap at the Fermi level, inducing a metal-insulator transition. Here, the authors report that a CDW gap resides in the unoccupied states but induces a topological metal-metal transition at the Fermi level in monolayer VS2.

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