Berlin 2024 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 12: 2D Materials I: Electronic Structure (joint session O/TT)
O 12.7: Vortrag
Montag, 18. März 2024, 16:30–16:45, MA 005
Unconventional charge-density-wave gap in monolayer NbS2 — Timo Knispel1, Jan Berges2, Arne Schobert3, Erik van Loon4, Wouter Jolie1, Tim Wehling3, Thomas Michely1, and •Jeison Fischer1 — 1II. Physikalisches Institut, Universität zu Köln, Köln — 2Universität Bremen, Bremen — 3I. Institut für Theoretische Physik, Universität Hamburg, Hamburg — 4Lund University, Lund, Sweden
Here, we report scanning tunneling microscopy and spectroscopy measurements for a monolayer of H-NbS2 grown by molecular beam epitaxy on graphene/Ir(111). We find that monolayer NbS2 displays a 3×3 modulation superstructure due to a charge density wave (CDW), which is not present in bulk NbS2. Evidence for the CDW is given by bias voltage contrast inversion and temperature suppression of the CDW signal. Our high-resolution differential conductance spectra display a pronounced gap of the order of 20 meV at the Fermi level. Within the gap low energy features are present. The gap structure with its low energy features is at variance with the expectation for a gap opening in the electronic band structure due to a static CDW distortion. Instead, comparison with ab initio calculations indicates that the observed gap structure is due to combined electron-phonon quasiparticles. The phonons in question are the elusive amplitude (Higgs) and phase (Goldstone) collective modes of the CDW transition [1].
[1] Knispel et al., arXiv:2307.13791.
Keywords: monolayer NbS2; charge density wave; scanning tunneling miscroscopy and spectroscopy; density functional theory; collective modes