Energy Gap and Electron Effective Mass in Chlorine Halide Superconductor at High Pressure

Dependences of the order parameter (Δ) and the electron effective mass (m_e^?) on the temperature for the chlorine halide superconductor are determined in the present work. The high values of the pressure (p₁=320 GPa and p₂=360 GPa), for which the critical temperature is equal to T_Cp1=30.6 K and T_Cp2=41.5 K, are taken into consideration. It is found that the dependence of the order parameter on the temperature deviates from the predictions of the classical Bardeen–Cooper–Schrieffer theory, due to the existence of the significant strong-coupling and retardation effects. The values of the order parameter, for the temperature close to zero Kelvin, are equal to Δ(0)_p1=4.89 meV and Δ(0)_p2=6.82 meV. The obtained results allowed next to calculate the dimensionless ratio R_Δ≡2Δ(0)/k_BT_C, which is equal to 3.71 and 3.81 in respect to p₁ and p₂. In the last step, it is proven that the electron effective mass is weakly dependent on the temperature in the area of the existence of the superconducting state and reaches its maximum at the critical temperature. For the considered values of the pressure, we obtain m_e^?_p1^max=1.69m_e and m_e^?_p2^max=1.78m_e, where the symbol m_e denotes the electron band mass.