R. Szczȩśniak

Theoretical description of the SrPt3P superconductor in the strong-coupling limit

The thermodynamic properties of a SrPt3P compound in the superconducting state have been investigated by taking the Eliashberg approach. The anti-perovskite SrPt3P is identified as a strong-coupling (λ = 1.33) s-wave superconductor with , where the zero-temperature energy gap () obtained from the Eliashberg calculations is 3.15 meV. The critical temperature TC was recently reported to be 8.4 K and this paper confirms the Coulomb pseudopotential repulsions () to be equal to 0.123. Moreover, the free energy difference between the superconducting and the normal state has been calculated. On the basis of the obtained results, the specific heat for the superconducting and the normal state, as well as the thermodynamic critical field, have been determined. It has been also proved that the electron effective mass is high and reaches its maximum equal to for the critical temperature.

Pseudogap in the Eliashberg approach based on electron‐phonon and electron‐electron‐phonon interaction

The properties of the superconducting and the anomalous normal state were described by using the Eliashberg method. The pairing mechanism was reproduced with the help of the Hamiltonian, which models the electron-phonon and the electron-electron-phonon interaction (EEPh). The set of the Eliashberg equations, which determines the order parameter function (φ), the wave function renormalization factor (Z), and the energy shift function (χ), was derived. It was proven that for the sufficiently large values of the EEPh potential, the doping dependence of the order parameter (φ/Z) has the analogous course to that observed experimentally in cuprates. The energy gap in the electron density of states is induced by Z and χ - the contribution from φ is negligible. The electron density of states possesses the characteristic asymmetric form and the pseudogap is observed above the critical temperature.

Characteristics of Superconducting State in Vanadium: the Eliashberg Equations and Semi-analytical Formulas

The superconducting state in vanadium characterizes with the critical temperature (Tc) equal to 5.3 K. The Coulomb pseudopotential, calculated with the help of the Eliashberg equations, possesses anomalously high value μ⋆(3Ωmax) = 0.259 or μ⋆(10Ωmax) = 0.368 (Ωmax denotes the maximum phonon frequency). Despite the relatively large electron-phonon coupling constant (λ = 0.91), the quantities such as the order parameter (Δ), the specific heat (C), and the thermodynamic critical field (Hc) determine the values of the dimensionless ratios not deviating much from the predictions of the BCS theory: RΔ = 2Δ(0)/kBTc = 3.68, RC = ΔC(Tc) /CN(Tc) = 1.69, and RH=TcCNTc/Hc20=0.171

Study of the superconducting phase in silicene under biaxial tensile strain

R_{H}=T_{c}C^{N}\left (T_{c}\right )\slash {H^{2}_{c}}\left (0\right )=0.171

Thermodynamic properties of antiperovskite MgCNi3 in superconducting phase

. This result is associated with the reduction of the strong-coupling and the retardation effects by the high value of the Coulomb pseudopotential. It has been shown that the results of the Eliashberg formalism can be relatively precisely reproduced with the help of the semi-analytical formulas, if the value of μ⋆ is determined on the basis of the Tc-Allen-Dynes expression (μAD⋆ = 0.198). The attention should be paid to the fact that in the numerical and in the semi-analytical approach the comparable values of the thermodynamic parameters for the same μ⋆ have been obtained only in the vicinity of the point μ⋆ = 0.1.