We consider a low-density electron-gas (rs equals 10 - 16) imbedded in a highly dispersive medium ((epsilon) 0/(epsilon) (infinity ) > 10). We find that the Fermi velocity is greatly enhanced over the single-particle value. This enhancement occurs only very close to the Fermi surface, within an energy range smaller than (omega) 0, the characteristic frequency of the dispersion. This theory applies to high-Tc cuprates, as well as to several other systems. It accounts for the highly-anomalous transport properties in the normal state. We believe that it also accounts for the high value of Tc, based on the standard phonon- mediated interaction BCS theory. There exist some experimental indications for a greatly- enhanced Fermi velocity in YBa2Cu3O7.
"Velocity renormalization in high-Tc cuprates", Proc. SPIE 2158, Oxide Superconductor Physics and Nano-Engineering, (10 August 1994); doi: 10.1117/12.182691; https://doi.org/10.1117/12.182691