Sum rules and electrodynamics of high-Tc cuprates in the pseudogap state -: art. no. 054516

We explore connections between the electronic density of states (DOS) in a conducting system and the frequency dependence of the scattering rate 1/tau(omega) inferred from infrared spectroscopy. We show that changes in the DOS upon the development of energy gaps can be reliably tracked through the examination of the 1/tau(omega) spectra using the sum rules discussed in the text. Applying this analysis to the charge dynarnics in high-T-c cuprates, we find radically different trends in the evolution of the DOS in the pseudogap state and in the superconducting state.