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. Special attention is paid to the influence of spin fluctuations in the ground state on the hole motion. It is shown that they reduce the bandwidth of the excitation energy as compared to the motion within the Neel ground state. The calculations are based on a cumulant approach to dynamical correlation functions introduced recently. This approach allows for a proper treatment of the strong electronic correlations which are incorporated in the model. It also guarantees that only spin fluctuations "connected" to the hole motion can contribute to the physical quantities.