CHARGE CORRELATIONS IN THE WEAKLY DOPED T-J MODEL CALCULATED BY PROJECTION TECHNIQUE

We study frequency- and wave-vector dependent charge correlations in w eakly doped antiferromagnets using Mori-Zwanzig projection technique. The system is described by the two-dimensional t-J model. The ground s tate is expressed within a cumulant formalism which has been successfu lly applied to study magnetic properties of the weakly doped system. W ithin this approach the ground state contains independent spin-bag qua siparticles (magnetic polarons). We present results for the charge-den sity response function and for the optical conductivity at zero temper ature for different values of t/J. They agree well with numerical resu lts calculated by exact diagonalization techniques. The density respon se function for intermediate and large moments shows a broad continuum on energy scales of order of several t whereas the optical conductivi ty for omega > 0 is dominated by low energy excitations (at 1.5-2J). W e show that these weak-doping properties can be well understood by tra nsitions between excited states of spin-bag quasiparticles.