Superconductivity in CuCl/Si superlattices: excitonic pairing?

Two-dimensional (2D) hetero-bonded semiconductor interfaces have been suggested as candidate geometries where excitonic superconductivity \footnote{V.L. Ginzburg, Sov. Phys. JETP {\bf 20},1549 (1965)} -- and the greatly enhanced where $T_C$ compared to phonon mechanisms mediation -- can be realized. Among experimental efforts, epitaxially grown CuCl on Si (111) has reportedly exhibited excitonic superconductivity at 60$\sim$150 K. Our first-principles calculations confirm 2D metallicity at the interfaces due to charge transfer by valence mismatch. \footnote{S.H. Rhim {\em et al.}, Phys. Rev. B {\bf 76}, 184505 (2007).} The excitonic mechanism is investigated by calculating the kernel function, $K(\omega)$, for the average of the electronic contributions to the effective interaction.\footnote{Zakharov {\em et al.}, J.Phys.Condes.Matter {\bf 9} 8501 (1997)} The attractive interaction found in the CuCl/Si superlattice indicates the feasibility of excitonic pairing for a certain frequency range.