Interface electronic structure, two-dimensional metallicity, and possible interface superconductivity in CuCl/Si superlattices

Results of highly precise all-electron full-potential linearized augmented plane wave density functional calculations demonstrate (i) two-dimensional metallicity, and (ii) possible superconductivity in CuCl/Si superlattices for [111] and [001] directions. The feature of two-dimensional (2D) metallicity arises from the charge transfer at the interfaces between CuCl and Si, where there is the valence charge imbalance. The 2D features are well evidenced by band structure, Fermi surfaces, and charge densities. Furthermore, to investigate possible superconductivity, we use McMillan [Phys. Rev. 167, 331 (1968)] formula to estimate TC, and evaluate the electron-phonon coupling constant, λ, using the rigid muffin-tin approximation. From our calculations, it is the interfaces that contribute to all intriguing physics: 2D metallicity, charge transfer, nonvanishing Hopfield [Phys. Rev. 186, 443 (1969)] parameter, and electron-phonon coupling. Moreover, our TC estimations (0.03-4.40 K) reveal that the electron-phonon coupling is too weak to account for the high TC (60-150 K) suggested in early experiments.