Strong electron–phonon coupling driven charge density wave states in stoichiometric 1T-VS2 crystals

Abstract

A charge density wave (CDW) transition is one of the fundamental quantum phenomena used to unveil the interactions between electrons and phonons that are coexisting or competing with other intriguing quantum phases, such as superconducting and ferromagnetic phases. Layered van der Waals materials, especially the family of vanadium dichalcogenides (VS₂, VSe₂, and VTe₂), have previously demonstrated CDW transition and ferromagnetic ordering, although these demonstrations lacked critical evidence. Among them, VS₂ single crystals in bulk form are challenging materials due to their thermodynamical instability; thus, experiments involving these materials have been rare. Herein, we report the multiple CDW states of a perfect 1T-phase VS₂ single crystal fabricated by chemical vapor transport and annealing treatment. The metastable phase comprising VS₂ and V₅S₈ turned into a stoichiometric 1T-phase VS₂ single crystal, confirmed by high-resolution microscopy. The fine structure formed at low temperature exhibits two clear CDW orders with the absence of nesting vectors on the Fermi surface, confirmed by scanning tunneling microscopy and density functional theory calculations. Our findings provide insight into obtaining a stable crystallographic phase of VS₂, stimulating further research into its compelling physical properties.