Drude weight and total optical weight in strongly correlated electron systems

Abstract

We study the doping dependence of the Drude weightD and the total optical weightK in strongly correlated electron systems described by at-t′-J model on a square lattice. Within a suitable 1/N expansion that includes leading quantum-fluctuation effects,D andK are found to increase linearly with small hole doping away from the Mott metal-insulator transition point at half-filling. The slow zero-sound velocity near the latter transition identifies with the velocity of the lower-energy branch of the twofold excitation spectrum. At higher doping values,D andK eventually saturate and then start to decreases. These features are in qualitative agreement with optical conductivity measurements in the high-T c cuprate superconductors.