Asymmetry in the Hole-Doped and Electron-Doped t-J Model

We model electron-doped high Tc materials using the t-t′-t′′-J model. This model is solved on a cluster with 32 sites using the method of exact diagonalization. Our purpose is to study the symmetry and asymmetry between hole- and electron-doped high Tc materials by comparing the results with those of the t-J model. In the electron-doped model with one charge carrier, we find a strong quasiparticle peak at (π,0). Compared to the t-J model, the bandwidth is larger, reflecting the fact that the charge carrier moves more freely in the electron-doped model. In the two-carrier model the ground state has robust dx2-y2 symmetry. This is in contrary to the two-hole t-J model whose ground state is a competition between low-energy states with dx2-y2 and p symmetries. The spatial distribution function of the carriers shows that they move almost freely on different sublattices.