Density response of the t-J model and renormalization of breathing and half-breathing phonon modes: A slave-fermion calculation

Abstract

The density fluctuation spectrum $N(\mathbf{k},\omega )$ is calculated for the t-J model in the low-doping regime using a slave-fermion method for the constrained fermions. The obtained results for $N(\mathbf{k},\omega )$ are in good agreement with diagonalization results. The density response is characterized by incoherent, momentum dependent spectral functions reaching up to energies $\sim 8t$ and a low-energy structure at energy $\sim J$ due to transitions in the quasiparticle band. $N(\mathbf{k},\omega )$ is shown to lead to a strong renormalization of planar bond-streching and breathing phonon modes with a large phonon linewidth at intermediate momenta caused by the low-energy response. Our results are consistent with recent neutron scattering data, showing the peculiar behavior of these modes.

4 pages, 3 figures, `Materials and Mechanisms of Superconductivity VI' conference, Houston, USA, Febr. 20-25, 2000