Strong Electron–Phonon Interaction Establishes Correlation between Superconducting and Charge Density Wave States in NbSe2

Here an analytical expression is proposed for the correlation between superconducting (SC) transition temperature (T_sc) derived by Louie and Cohen and charge density wave (CDW) transition temperature derived by Peierls at strong electron–phonon interaction. This expression was verified by the pressure effect T_sc and T_cdw of 2H-NbSe₂ with m ˜ 64.86 and c ˜ 2.24 as best-fitting parameters. From these parameters, phonon energies h√ω²_sc ˜ 3.8 meV and hω_cdw ˜ 1.4 meV were calculated for SC and CDW states respectively. It also provides T_cdw very close to the experimental values of 2H- and 4H-NbSe₂, regardless of their stacking order and coordination difference.