Electronic and superconducting properties of silicon and carbon clathrates

We review the electronic properties of pure and doped silicon and carbon clathrates. Using accurate quasiparticle calculations within the GW approximation, we show that undoped clathrates are ∼1.8 eV band gap semiconducting compounds. Further, the effect of doping by elements more electronegative than Si is shown to lead to p-type doped semiconductors with a ∼2.3-2.5 eV band gap in the visible energy range. Similar results are observed under doping of hydrogenated Sin (n=20,24,28) clusters and rationalized on the basis of group theory analysis. Finally, the superconducting properties of doped clathrates are discussed. We show that superconductivity is an intrinsic property of the standard silicon sp3 environment provided that efficient doping can be achieved