Electron-phonon coupling and the Coexistence of Superconductivity and Charge-Density Wave in Monolayer NbSe2

Abstract

Monolayer 2H-NbSe2 has recently been shown to be a 2-dimensional superconductor, with a coexisting charge-density wave (CDW). As both phenomena are intimately related to electron-lattice interaction, a natural question is how superconductivity and CDW are interrelated through electron-phonon coupling (EPC), which is important to the understanding of 2-dimensional superconductivity. This work investigates the superconductivity of monolayer NbSe2 in CDW phase using the anisotropic Migdal-Eliashberg formalism based on first principles calculations. The mechanism of the competition between and coexistence of the superconductivity and CDW is studied in detail by analyzing EPC. It is found that the intra-pocket scattering is related to superconductivity, leading to almost constant value of superconducting gaps on parts of the Fermi surface. The inter-pocket scattering is found to be responsible for CDW, leading to partial or full bandgap on the remaining Fermi surface. Recent experiment indicates that there is transitioning from regular superconductivity in thin-film NbSe2 to two-gap superconductivity in the bulk, which is shown here to have its origin in the extent of Fermi surface gapping of K and K' pockets induced by CDW. Overall blue shifts of the phonons and sharp decrease of Eliashberg spectrum are found when the CDW forms.

12 pages, 13 figures in total. Accepted, Physical Review B (Rapid Communication) (2019)

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• Direct observation of competition between superconductivity and charge density wave order in YBa2Cu3Oy
• Fermi surface nesting and the origin of Charge Density Waves in metals
• Classification of Charge Density Waves Based on Their Nature
• Origin of superconductivity and latent charge density wave in NbS${}_2$
• Electron-phonon interaction and transport properties of metallic bulk and monolayer transition metal dichalcogenide TaS${}_2$

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• Friedel oscillations and chiral superconductivity in monolayer NbSe${}_2$
• Effects of 3 MeV Proton Irradiation on Superconductivity and CDW in 2H-NbSe2 Single Crystals
• Charge Orders in Fully Intercalated Bilayer TaSe${}_2$: Dependence on Interlayer Stacking and Intercalation Sites
• Real-space topology and charge order in the Haldane-Holstein Model
• Unconventional superconductivity in monolayer transition metal dichalcogenides
• Interlayer coupling driven stabilization and superconductivity in bilayer CoTe${}_2$
• Giant Kohn anomaly and chiral phonons in the charge density wave phase of 1H-NbSe${}_2$
• Supercurrent effect in a charge density wave intertwined superconductor