The thermodynamic properties of the MgB2 superconductor: The two-band Eliashberg equations

In the present paper it was shown that the critical value of the Coulomb pseudopotential (μC∗) for MgB2 is 0.03578; the calculated value of μC∗ 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 μC∗=0.03578, for the selected values of temperature, the order parameters for σσ and ππ band (ΔσΔσ and ΔπΔπ) as well as the wave function renormalization factors (ZσZσ and ZπZπ) were calculated. The ratios Ra≡2Δa(0)/kBTC were estimated, where aa is the band index and TCTC is a value of the critical temperature. Values of Rσ=4.24Rσ=4.24 and Rπ=1.54Rπ=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 σσ and ππ band were estimated for TCTC; [Zσ]ω=0=2.32[Zσ]ω=0=2.32 and [Zπ]ω=0=1.63[Zπ]ω=0=1.63. Obtained results were compared with experimental data and with the other theoretical predictions.