Dichotomy of charge density wave and superconductivity in monolayer NbS2 and NbSe2: A view from fermiology

Abstract

The interplay of charge-density wave (CDW) and superconductivity is a key issue in low-dimensional materials, whereas it has yet to be clarified even in simple two-dimensional materials such as monolayer transition-metal dichalcogenide. We fabricated a monolayer 1H-NbS2 film on bilayer graphene/SiC(0001) by combining the molecular-beam epitaxy and topotactic chemical reaction, and investigated the electronic structure by angle-resolved photoemission spectroscopy in collaboration with first-principles calculation. We found that although the Fermi surface of monolayer 1H-NbS2 consists of large hole pockets centered at the Γ and K points similarly to isostructural monolayer 1H-NbSe2, the shape of the pocket at the K point is more triangular shaped in NbS2. Scanning tunneling microscopy and transport measurements at low temperature show no evidence for CDW or superconductivity in NbS2 in stark contrast to NbSe2. The degradation of CDW in NbS2 is likely caused by the suppression of quasiparticle scattering between the hot spots connected by the 2/3ΓM nesting vector associated with the change in the shape of the K-centered pocket. The present results suggest the highly susceptible nature of CDW and superconductivity to the subtle change of the fermiology in Nb dichalcogenides.

Source-reported materials — not catalogue approval

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