2025/01/14 by Amjad Al Taleb, Taleb, Amjad Al, Wen Wan +7
Physics and Astronomy · #FOS: Physical sciences #Materials Science (cond-mat.mtrl-sci) #Mesoscale and Nanoscale Physics (cond-mat.mes-hall) #Physics of Superconductivity and Magnetism #Quantum and electron transport phenomena #Strongly Correlated Electrons (cond-mat.str-el) #Superconductivity (cond-mat.supr-con) #Topological Materials and Phenomena
paper · pdf · doi:10.48550/arxiv.2501.08140
openalex publication_date 2025/01/14 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
The interplay between substrate interactions and electron-phonon coupling in two-dimensional (2D) materials presents a significant challenge in understanding and controlling their electronic properties. Here, we present a comparative study of the structural characteristics, phonon dynamics, and electron-phonon interactions in bulk and monolayer NbSe2 on epitaxial bilayer graphene (BLG) using helium atom scattering (HAS). High-resolution helium diffraction reveals a (9x9)0∘ superstructure within the NbSe2 monolayer, commensurate with the BLG lattice, while out-of-plane HAS diffraction spectra indicate a low-corrugated (3√(3)x3√(3))30∘ substructure. By monitoring the thermal attenuation of the specular peak across a temperature range of 100 K to 300 K, we determined the electron-phonon coupling constant λHAS as 0.76 for bulk 2H-NbSe2. In contrast, the NbSe2 monolayer on graphene exhibits a reduced λHAS of 0.55, corresponding to a superconducting critical temperature (TC) of 1.56 K according to the MacMillan formula, consistent with transport measurement findings. Inelastic HAS data provide, besides a set of dispersion curves of acoustic and lower optical phonons, a soft, dispersionless branch of phonons at 1.7 meV, attributed to the interface localized defects distributed with the superstructure period, and thus termed moiré phonons. Our data show that moiré phonons contribute significantly to the electron-phonon coupling in monolayer NbSe2. These results highlight the crucial role of the BLG on the electron-phonon coupling in monolayer NbSe2, attributed to enhanced charge transfer effects, providing valuable insights into substrate-dependent electronic interactions in 2D superconductors.