ABSTRACT

A review is given for the theoretical framework to give a reliable prediction of the superconducting transition temperature (Tc) from first principles, together with a practical strategy for its application to actual materials with illustrations of the results of Tc calculated for superconductors in the weak-coupling region like the alkali-and alkaline-earth-intercalated graphites as well as those in the strong-coupling region like the alkali-doped fullerides. 8.1 IntroductionIn quantum mechanics, a ground state is determined through a compromise between the kinetic energy (which makes particles itinerant) and the potential energy (which makes them localized). If the latter includes the interaction between particles, there appears

c a further complication due to their correlated motion. In elucidating the microscopic mechanism of superconductivity, this intrinsic complexity in quantum mechanics cannot be avoided but is even more intensified, specifically because superconductivity is a phenomenon in which an assembly of electrons, negatively charged particles with one-half spin, goes into the pair-condensed phase as a consequence of the dominance of some effective attractions between electrons mediated by either phonons, plasmons, spin-fluctuations, or orbitalfluctuations over the short-range Coulomb repulsions, indicating the necessity of deeply understanding and carefully investigating the physics of this charge-spin-phonon (-orbital) complex before making a reliable evaluation of the transition temperature Tc of this second-order phase transition. Thus one would imagine that the task of reliably calculating Tc must be formidably difficult, but the ultimate goal in the theoretical study of high-Tc superconductivity should be to construct a good theoretical framework for an accurate prediction of Tc; without such a theoretical tool, we could never conduct a research directly and intimately touched with the most salient feature of high-Tc materials, namely, the very feature that Tcbecomes very high in those materials.