Quasiparticle Spectra, Charge-Density Waves, Superconductivity, and Electron-Phonon Coupling in2H−NbSe2

High-resolution photoemission has been used to study the electronic structure of the charge-density wave (CDW) and superconducting dichalcogenide, $2\mathrm{H}\mathrm{\text{−}}{\mathrm{N}\mathrm{b}\mathrm{S}\mathrm{e}}_2$. From the extracted self-energies, important components of the quasiparticle interactions have been identified. In contrast to previously studied ${\mathrm{T}\mathrm{a}\mathrm{S}\mathrm{e}}_2$, the CDW transition does not affect the electronic properties significantly. The electron-phonon coupling is identified as a dominant contribution to the quasiparticle self-energy and is shown to be very anisotropic ($k$ dependent) and much stronger than in ${\mathrm{T}\mathrm{a}\mathrm{S}\mathrm{e}}_2$.