Superconductivity from Holes in CeCu2Si2

One of the fascinating facts about superconductivity is that despite more than 100 years of extensive research and 7 Nobel prizes, we are still away from our main goals. The race continues to both achieving room temperature superconductivity as well as to obtain a novel theory of attractive potential between electrons. By now we know two mechanisms for attractive interaction between the same-charge fermions: Meson mediates an attraction between protons. Phonon mediates attractive potential between electrons with superconductivity. In this talk, I will present a new mechanism of attractive potential between electrons, forming superconductivity. The basic principle is as follows. The flat bands or f-orbitals have strong Coulomb interaction, which prohibit double occupancy. However, the unoccupied f-site can be occupied by a conduction electron since the presence of valence fluctuation channel allows mutation between the f- and conduction electrons. We show that the doubly occupied state with f- and conduction electrons condensates like a Cooper pair. I will present this theory along with detailed comparison with recent experimental surprises of conventional superconductivity in heavy-fermion materials where decades old studies predicted unconventional superconductivity.