Anisotropic Eliashberg theory for superconductivity in compressed and doped MgB2

We have studied superconducting properties of compressed and doped MgB2 by performing first-principles calculations of the normal material properties and by solving the fully anisotropic Eliashberg equations. At each pressure or doping, electronic structures, phonon spectra, and momentum-dependent electron-phonon coupling strengths are calculated. Then using the fully anisotropic Eliashberg equations, the superconducting transition temperatures (Tc), the superconducting energy gaps [Δ (k)], and the specific heats are obtained. Our results show that the multiple-gap nature of Δ (k) in MgB2 is robust with applied pressure although Tc and Δ (k) decrease substantially and that electron doping reduces Tc and degrades severely the superconducting energy gap in the π bands.