The thermodynamic properties of the superconductor: The two-band Eliashberg equations

In the present paper it was shown that the critical value of the Coulomb pseudopotential ( μ C ∗ ) for MgB2 is 0.03578; the calculated value of μ C ∗ essentially differs from the value given by G.A. Ummarino et al. [G.A. Ummarino, R.S. Gonnelli, S. Massidda, A. Bianconi, Physica C 407 (2004) 121]. Assuming μ C ∗ = 0.03578 , for the selected values of temperature, the order parameters for σ and π band ( Δ σ and Δ π ) as well as the wave function renormalization factors ( Z σ and Z π ) were calculated. The ratios R a ≡ 2 Δ a ( 0 ) / k B T C were estimated, where a is the band index and T C is a value of the critical temperature. Values of R σ = 4.24 and R π = 1.54 were obtained. In the present work a total normalized density of states function was also calculated. In the last step the values of the wave function renormalization factors that define effective mass of electrons from the σ and π band were estimated for T C ; [ Z σ ] ω = 0 = 2.32 and [ Z π ] ω = 0 = 1.63 . Obtained results were compared with experimental data and with the other theoretical predictions.