A study was made of the superconducting properties of MgB2 from first-principles under isotropic, uniaxial and biaxial compression. It was found that the in-plane B phonons near the zone-center were very anharmonic and strongly coupled to the planar B σ bands near the Fermi level. This mode was found to be the key to quantitatively explain the observed high TC, the total isotope effect and the pressure dependence of TC. It was proposed that a stringent test on the hole and phonon based theories of the superconductivity in MgB2 would be a measurement of the biaxial ab-compression dependence of TC.

A Simple Theory of 40K Superconductivity in MgB2 - First-Principles Calculations of TC, its Dependence on Boron Mass and Pressure. T.Yildirim, O.Gülseren: Journal of Physics and Chemistry of Solids, 2002, 63[12], 2201-6