Thermodynamics of the CaLi₂ Superconductor in the Vicinity of Structural Phase Transition

Eliashberg formalism is used to investigate the thermodynamic properties of the high-pressure superconducting phase of the CaLi₂ compound. In particular, our calculations are conducted in the vicinity of the C2/c →P2₁/c pressure-induced structural phase transition. We show that, in the considered case, the value of the Coulomb pseudopotential is high and equals 0.26. Moreover, we give the analysis of the thermodynamic parameters such as the superconducting transition temperature (T_C), the energy gap at the Fermi level (2Δ(0)), the thermodynamic critical field (H_C), and the specific heat of superconducting (C^S) and normal (C^N) states. We emphasize that the characteristic dimensionless ratios R_Δ ≡2Δ(0)/k_BT_C, R_H≡T_CC^N(T_C)/H_C²(0), and R_C≡ΔC(T_C)/C^N(T_C), have values that are beyond the predictions of the BCS theory in the case of the considered material. In particular, R_Δ=3.85, R_H=0.161, and R_C=1.86. Furthermore, it is proved that the effective electron mass is high and equals 2.02m_e, where m_e denotes the bare electron mass.