




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 
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 densityfunctionaltype 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 materialspecific properties such as the critical temperature. To this end, the electronphonon interaction and the electronelectron 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 densityfunctional theory for electrons and nuclei.
Approximations of the universal xc functionals are derived on the basis of manybody perturbation theory. Numerical results for the critical temperature and the gap will be presented for simple metals, for MgB_{2}, and for Li, Al and K under pressure. In particular, for MgB_{2}, 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 CaC_{6} will be discussed. 





