CUMULANT APPROACH TO THE COHERENT HOLE MOTION IN THE T-J MODEL

We discuss the motion of a hole generated in the Cu - O plane in high temperature superconductors at half-filling. The system is described by the t - J model. It is shown that spin fluctuations in the ground state reduce the bandwidth of the excitation energy as compared to the motion within the Neel ground state. The calculations are based on a recently introduced cumulant approach to dynamical correlation functions. This approach allows for a proper treatment of the strong electronic correlations. It also guarantees that only spin fluctuations 'connected' to the hole motion can contribute to the physical quantities.