Density response of cuprates and renormalization of breathing phonons

Abstract

We analyse the dynamical density fluctuation spectra for cuprates starting from the $t-J$ model in a slave-boson 1/N representation. The results obtained are consistent with diagonalization studies and show novel low-energy structure on the energy scale $J+\delta t$ due to the correlated motion of holes in a RVB spin liquid. The low-energy response implies an anomalous renormalization of several phonon modes. Here we discuss the renormalization of the highest breathing phonons in La${}_{2-x}$Sr${}_x$CuO${}_4$.

10 pages and 8 figures, talk given at NATO Advanced Research Workshop, Bled, Slovenia, 26-30 April 2000