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

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.

References in corpus (8)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Advanced capabilities for materials modelling with Quantum ESPRESSO
• Fermi surface nesting and the origin of Charge Density Waves in metals
• Nonlinear lattice dynamics as a basis for enhanced superconductivity in YBa2Cu3O6.5
• Two energy gaps and Fermi surface 'arcs' in NbSe2
• Evidence of Spin Frustration in Vanadium Diselenide Monolayer Magnet
• Fermi surface nesting in several transition metal dichalcogenides
• Substrate-induced suppression of charge density wave in monolayer 1H-TaS2 on Au(111)