Enhancement of the superconducting transition temperatures in ion-implanted aluminium alloys

Random alloys of C, Si, and Ge with Al, prepared by ion implantation at liquid helium temperatures, have maximum superconducting transition temperatures Tc of 4.2 K (C), 7.35 K (Ge) and 8.35 K (Si). The latter value is the highest yet obtained for an Al-based alloy. All these values are obtained for covalent element concentrations of ∼ 25 %. The effect of lattice disorder is not found sufficient to account for the observed Tc enhancements.