High-pressure superconductivity in yttrium: The strong-coupling approach

In the framework of the Eliashberg formalism, the properties of the superconducting state inducing in yttrium for the pressure at p1≡26GPa and p2≡31GPa([TC]p1=7.9Kand[TC]p2=9.27K) have been determined. It has been proven that the value of the Coulomb pseudopotential is high and increases with the increasing pressure: [μ⋆]p1=0.181 and [μ⋆]p2=0.251. Next, the order parameter (Δ(T)), the thermodynamic critical field (HC(T)), the specific heat in the superconducting state (CS(T)), and the specific heat in the normal state (CN(T)) have been calculated. It has been proven that the values of the dimensionless parameters RΔ≡2Δ(0)kBTC,RC≡CS(TC)−CN(TC)CN(TC), and RH≡TCCN(TC)HC2(0) significantly deviate from the predictions of the classical BCS theory: RΔ∈{3.97,4.13},RC∈{2.16,2.41}, and RH∈{0.153,0.152}. The electron effective mass is high for both pressures [me⋆]p1T=TC=2.16me and [me⋆]p2T=TC=2.64me, where the symbol me denotes the electron band mass.