A study was made of the variation of TC as a function of charge density and lattice parameters in Mg1-xAlxB2 superconducting samples. The AB2 heterostructure of metallic B layers (intercalated by A = Mg, Al layers, playing the role of spacers) was made by direct chemical reaction. The spacing between B layers and their charge density were controlled by chemical substitution of Mg by Al atoms. It was shown that high TC superconductivity was realized by tuning the chemical potential at a so-called shape resonance. The energy width of the superconducting shape resonance was found to be about 400meV.

A Superconductor Made by a Metal Heterostructure at the Atomic Limit Tuned at the ‘Shape Resonance’ - MgB2. A.Bianconi, D.Di Castro, S.Agrestini, G.Campi, N.L.Saini, A.Saccone, S.De Negri, M.Giovannini: Journal of Physics - Condensed Matter, 2002, 13, 7383-90