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Electron-phonon coupling and two-band superconductivity of AI- and C-doped MgB_2

机译:AI和C掺杂的MgB_2的电子声子耦合和两带超导

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We have studied the electron-phonon and superconducting properties of the Mg_(1-x)Al_xB_2 and MgB_(2(1-y))C_(2y) alloys within the framework of density-functional theory using the self-consistent virtual-crystal approximation. For both alloys, the Eliashberg spectral functions and the electron-phonon coupling constants have been calculated in the two-band model for several concentrations up to x(Al)=0.55 and y(C)=0.175. We solved numerically the two-band Eliashberg gap equations without considering interband scattering. Using a single parameter for the Coulomb pseudopotential, which was determined for the undoped compound, we were able to reproduce the experimental doping dependence of △_σ, △_π, and T_c for both alloys on a quantitative level. In particular, the observed differences in the doping range of superconductivity between Al and C doping indicate a pronounced influence of the doping site, which can be explained naturally in the present approach without the need to invoke interband scattering, suggesting that this factor plays only a minor role.
机译:我们使用自洽虚拟晶体在密度泛函理论框架内研究了Mg_(1-x)Al_xB_2和MgB_(2(1-y))C_(2y)合金的电子声子和超导性能近似。对于两种合金,已经在两波段模型中针对x(Al)= 0.55和y(C)= 0.175的几种浓度计算了Eliashberg光谱函数和电子-声子耦合常数。我们在不考虑频带间散射的情况下,通过数值方法求解了两频带Eliashberg间隙方程。使用针对未掺杂化合物确定的库仑伪电位的单个参数,我们能够在定量水平上重现两种合金的实验掺杂依赖性△_σ,△_π和T_c。特别地,观察到的Al和C掺杂之间超导掺杂范围的差异表明了掺杂位点的显着影响,这在本方法中可以自然地解释而无需引起带间散射,这表明该因素仅起次要角色。

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