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21世紀COEセミナー「How to calculate the critical temperature of superconductors ?」

日時 平成19年(2007年)5月16日(水)13:00〜
場所 理学研究科H棟7階 大セミナー室 (H701)
講師 E.K.U. Gross 教授(Freie Universitaet Berlin・ドイツ)
題目 How to calculate the critical temperature of superconductors ?
概要 A novel density-functional-type approach to the description of phonon- mediated superconductivity is presented. The goal of this approach is to provide a theory with predictive power, allowing the calculation of material-specific properties such as the critical temperature. To this end, the electron-phonon interaction and the electron-electron repulsion are treated on the same footing. There are no adjustable parameters such as the μ* of Eliashberg theory. The formalism can be viewed as the superconducting generalization of the multi- component density-functional theory for electrons and nuclei.
Approximations of the universal xc functionals are derived on the basis of many-body perturbation theory. Numerical results for the critical temperature and the gap will be presented for simple metals, for MgB2, and for Li, Al and K under pressure. In particular, for MgB2, the two gaps and the specific heat as function of temperature are in very good agreement with experimental data. For Li and Al under pressure the calculations explain why these two metals behave very differently, leading to a strong enhancement of superconductivity for Li and to a clear suppression for Al with increasing pressure. For K we predict a behavior similar to Li, i.e. a strong increase of Tc with increasing pressure. Finally, the peculiar features of the superconducting phase of CaC6 will be discussed.

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