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TT: Fachverband Tiefe Temperaturen

TT 14: Superconductivity: Non-Cuprate Non-Ferropnictide Superconductors

TT 14.1: Vortrag

Dienstag, 24. März 2009, 09:30–09:45, HSZ 105

First principles study of Al and C-doped MgB₂: evolution of two gaps and critical temperature — •omar de la peña-seaman^1,2, romeo de coss², klaus-peter bohnen¹, and rolf heid¹ — ¹Institut für Festkörperphysik, Forschungszentrum Karlsruhe, Germany — ²Department of Applied Physics, Cinvestav-Merida, Mexico

We have studied the electron-phonon and superconducting properties of the Mg_1−xAl_xB₂ and MgB_2(1−x)C_2x alloys within the framework of density functional perturbation theory, using a mixed-basis pseudopotential method and the virtual crystal approximation (VCA) for modeling the alloys. For both systems, the Eliashberg spectral function (α²F(ω)) and the electron-phonon coupling parameter (λ) have been calculated in the two band model (σ,π) for several concentrations until x(Al)=0.55 and x(C)=0.175. Using the calculated α_ij²F(ω) and a diagonal expression for the Coulomb pseudopotential matrix, µ^*, we solved numerically the Eliashberg gap equations in the two band model without interband scattering. We reproduce the experimental decreasing behavior of Δ_σ(x), Δ_π(x), and T_c(x) for both alloy systems. The role of the interband scattering in the observed behavior of the superconducting gaps and T_c in the Al- and C-MgB₂ alloys is discussed.