The superconducting phase of calcium under the pressure at 200 GPa: The strong-coupling description

The thermodynamic parameters of the superconducting state in calcium under the pressure at 200 GPa have been determined. The numerical analysis by using the Eliashberg equations in the mixed representation has been conducted. It has been stated that the critical temperature (TC) decreases from 36.15 K to 20.79 K dependently on the assumed value of the Coulomb pseudopotential (μ⁎∈〈0.1,0.3〉μ⁎∈〈0.1,0.3〉). Next, the order parameter near the temperature of zero Kelvin (Δ(0)Δ(0)) has been obtained. It has been proven that the dimensionless ratio 2Δ(0)/kBTC2Δ(0)/kBTC decreases from 4.25 to 3.90 together with the growth of μ⁎μ⁎. Finally, the ratio of the electron effective mass to the electron bare mass (me⁎/me) has been calculated. It has been shown that me⁎/me takes the high value in the whole range of the superconducting phase's existence, and its maximum is equal to 2.23 for T=TCT=TC.

► Thermodynamic parameters of the superconducting state that induces in calcium under the pressure at 200 GPa.
► The high critical temperature.
► The non-BCS value of the ratio 2Δ/kBTC2Δ/kBTC.
► The large electron effective mass.