Charge Density Wave and Electron-Phonon Interaction in Epitaxial Monolayer NbSe<sub>2</sub> Films
Xuedong Xie, Dongjing Lin, Li Zhu, Qiyuan Li, Junyu Zong, Wang Chen, Qinghao Meng, Qichao Tian, Shao‐Chun Li, Xiaoxiang Xi, Can Wang, Yi Zhang
Abstract
Understanding the interplay between superconductivity and charge-density wave (CDW) in NbSe 2 is vital for both fundamental physics and future device applications. Here, combining scanning tunneling microscopy, angle-resolved photoemission spectroscopy and Raman spectroscopy, we study the CDW phase in the monolayer NbSe 2 films grown on various substrates of bilayer graphene (BLG), SrTiO 3 (111), and Al 2 O 3 (0001). It is found that the two stable CDW states of monolayer NbSe 2 can coexist on NbSe 2 /BLG surface at liquid-nitrogen temperature. For the NbSe 2 /SrTiO 3 (111) sample, the unidirectional CDW regions own the kinks at ±41 meV and a wider gap at 4.2 K. It is revealed that the charge transfer from the substrates to the grown films will influence the configurations of the Fermi surface, and induce a 130 meV lift-up of the Fermi level with a shrink of the Fermi pockets in NbSe 2 /SrTiO 3 (111) compared with the NbSe 2 /BLG. Combining the temperature-dependent Raman experiments, we suggest that the electron-phonon coupling in monolayer NbSe 2 dominates its CDW phase transition.