A superconductor made by a metal heterostructure at the atomic limit tunedat the 'shape resonance': MgB2

We have studied the variation of superconducting critical temperature T-c a s a function of charge density and lattice parameters in Mg1-xAlxB2 superco nducting samples. The AB(2) heterostucture of metallic boron layers (interc alated by A = magnesium, aluminum layers, playing the role of spacers) is m ade by direct chemical reaction. The spacing between boron layers and their charge density are controlled by chemical substitution of Mg by Al atoms. We show that high T-c superconductivity is realized by tuning the chemical potential at a `shape resonance' according with the patent for `high-temper ature superconductors made by metal heterostructures at the atomic limit'. The energy width of the superconducting shape resonance is found to be abou t 400 meV.