Overscreening mechanism for room temperature superconductivity

My view for room temperature superconductivity and a mechanism for the superconductivity are presented. The common and different points for conventional and high Tc copper-oxide superconductors are discussed. In the oxides the conduction-carrier concentrations are relatively small and the highly correlated carriers strongly interact with lattice vibrations. As a result, the dispersion of the in-plan Cu–O bond-stretching longitudinal optical phonon mode is strongly softened near the Brillouin zone boundary, as seen in the experiments of neutron scattering and photoemission. It can be described with a negative dielectric-function that results in an overscreening of the intersite Coulomb interaction due to phonon-induced charge transfer and vibronic electron phonon resonance. The Coulomb interaction renormalized by the overscreening effect works for an attractive interaction between carriers in regions near the zone boundary. The interaction generates the superconductivity with the transition temperature well in excess of 100 K. On the basis of the overscreening mechanism, we propose the following guiding principle for searching materials with superconducting transition temperatures above the room temperature. The materials should have relatively small conduction-carrier concentrations, and thus the systems are of highly correlated. The materials should contain light atoms that have large lattice vibration amplitudes, and the carriers interact strongly with vibrating atoms.