DENSITY-FLUCTUATIONS AND PHONON RENORMALIZATION IN THE T-J MODEL

The density response function of the t-J model is studied starting fro m a mixed gauge formulation of the slave boson approach. The theory pr edicts a low energy structure in a density response at large momenta. The physical origin of this excitation is due to the formation of a na rrow polaron-like band of dressed holes. We consider also the renormal ization of phonons coupled to the density fluctuations, and explain th e unusual doping dependence of breathing and bond-stretching oxygen ph onons in cuprates.