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Keywords:

  • Ca Pnma phase;
  • high-pressure effects;
  • superconductivity;
  • thermodynamic properties

Abstract

The thermodynamic parameters of the superconducting state in calcium under the pressure of 161 GPa have been calculated within the framework of the Eliashberg approach. It has been shown that the value of the Coulomb pseudopotential is high (equation image) and the critical temperature (TC = 25 K) should be determined from the modified Allen–Dynes formula. In addition, it has been found that the basic dimensionless ratios of the thermodynamic parameters significantly diverge from the BCS predictions, and take the following values: (i) The zero-temperature energy gap to the critical temperature (equation image) is equal to 4.01. (ii) The ratio equation image equals 2.17, where CS and CN denote the specific heats for the superconducting and normal states, respectively. (iii) The quantity equation image, where HC indicates the thermodynamic critical field. Finally, it has been proven that the electron effective mass is large and takes the maximum of 2.32me at TC.