Characterization of the high-pressure superconductivity in the Pnma phase of calcium

TL;DR

This study analyzes the thermodynamic properties of calcium's high-pressure superconducting phase at 161 GPa using Eliashberg theory, revealing significant deviations from BCS predictions and highlighting a large electron effective mass.

Contribution

The paper provides a detailed thermodynamic characterization of calcium's superconductivity under high pressure using Eliashberg calculations, including the impact of a high Coulomb pseudopotential.

Findings

Critical temperature is 25 K at 161 GPa.

Dimensionless ratios significantly diverge from BCS values.

Electron effective mass peaks at 2.32 times the electron mass.

Abstract

The thermodynamic parameters of the superconducting state in calcium under the pressure at 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 (0.24) and the critical temperature (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(R1) is equal to 4.01. (ii) The ratio R2 equals 2.17. (iii) The quantity R3=0.158. Finally, it has been proven that the electron effective mass is large and takes the maximum of 2.32*me at TC.