SINGLE HOLE IN A QUANTUM ANTIFERROMAGNET - FINITE-SIZE-SCALING APPROACH

Exact diagonalizations of small clusters up to 26 sites are used to extrapolate the ground-state energy of a single hole in the Neel state of the t-J(z) model or in the quantum antiferromagnetic (t-J model. A surprisingly rapid convergence with system size is observed for a wide range of parameters and for the largest clusters considered. In the Ising limit the energy dependence with J(z) is remarkably close to a J(z)2/3 law for intermediate coupling in agreement with Brinkman-Rice type of calculations. Nevertheless a small but significant bandwidth indicates that the hole can propagate coherently in this limit. Clearly the polaronic behavior approximately J(z)1/2, for very small J(z), is out of the range of the method. When quantum fluctuations are introduced (isotropic case) the ground-state energy behavior still remains close to that of the Ising limit although an overall increase of the energy by a factor 0.3t is observed. This suggests that the "string scenario" might have some relevance there.