Electronic structure and superconducting gap of silicon clathrate Ba8Si46 studied with ultrahigh-resolution photoemission spectroscopy - art. no. 172504

We study the electronic structure and superconducting transition of silicon clathrate Ba8Si46 (T-c = 8 K) using photoemission spectroscopy. We observe a narrow band at the Fermi level (E-F), whose width (similar to0.3 eV) is substantially smaller than that of band structure calculations (similar to1 .5 eV). Ultrahigh-resolution measurements show a superconducting gap at 5.4 K [2 Delta (0)/k(B)T(c)=3.51]. Fine structures associated with phonons are observed within 70 meV of E-F. These results characterize Ba8Si46 as a wea k-coupling superconductor most probably driven by phonon.