Ga-doping effect on superconductivity for Ba8Si46 clathrates

We present a joint experimental and theoretical study of the superconductivity and electronic structures in type-I Ga-doped silicon clathrates. The superconducting critical temperature in Ba8Si46-xGax is shown to decrease strongly with gallium content increasing. These results are corroborated by first-principles simulations calculated from the density-functional theory with plane waves and pseudopotentials. The simulations show that Ga doping results in a large decrease of electronic density of states in Fermi level, which can explain the superconducting critical temperature decrease with Ga-doping in the BCS theoretical frame.