Critical temperature Tc versus charging energy Ec in MgB2 and C60/CHBr3

Abstract The boride compounds MB x related to the magnesium–boron stacking layered material MgB 2 are discussed in terms of the B–B layers in the borides analogous to the Cu–O ones in the cuprates. We propose a possibility of superconducting materials which exhibit higher critical temperature T c than 39 K of MgB 2 . We point out a role of interstitial ionic atoms M (e.g., Mg in MgB 2 ) as capacitors, which reduce the condensation-energy loss due to the charging energy E c between the B and B layers. In the viewpoint of the present model, the recently discovered 117-K superconductor C 60 /CHBr 3 is also discussed in terms of the intercalation molecules CHBr 3 as possible capacitors among the superconducting grains of C 60 molecules.