Superconductivity in α-polonium at the reduced volume

The paper discusses the thermodynamic properties of the superconducting state that gets induced in the α phase of polonium at the reduced volume (V/Vexp=0.93). It has been shown that the critical temperature (TC) is equal to 7.11 K, if the assumed value of the Coulomb pseudopotential equals 0.1. Then, the thermodynamic critical field (HC) has been calculated, as well as the specific heat in the superconducting state (CS) and in the normal state (CN). It has been proven that the values of the dimensionless ratios RH≡TCCN(TC)/HC2(0) and RC≡ΔC(TC)/CN(TC) differ significantly from the expectations of the BCS theory. In particular, RH=0.147 and RC=2.34. In the next step, the order parameter (Δ) and the electron effective mass have been calculated. It has been found that the ratio of the energy gap to the critical temperature significantly exceeds the value predicted by the BCS model: RΔ≡2Δ(0)/kBTC=4.12. The electron effective mass is high and reaches its maximum equal to 2.191me at the critical temperature, where the parameter me denotes the electron band mass. Nevertheless, some recent papers show that α-polonium becomes unstable for V/Vexp lower or equal to 0.97. In this case, our study relates to the unstable hypothetical phase.