Proposal of an extended t-J Hamiltonian for high-Tc cuprates from ab initio calculations on embedded clusters

Abstract

A series of accurate ab initio calculations on CupOq finite clusters, properly embedded in the Madelung potential of the infinite lattice, have been performed in order to determine the local effective interactions in the CuO2 planes of La22xSrxCuO4 compounds. The values of the first-neighbor interactions, magnetic coupling (JNN5125 meV!, and hopping integral (tNN52555 meV! have been confirmed. Important additional effects are evidenced, concerning essentially the second-neighbor hopping integral tNNN51110 meV, the displacement of a singlet toward an adjacent colinear hole, hSD abc5280 meV, a non-negligible hole-hole repulsion VNN2VNNN50.8 eV, and a strong anisotropic effect of the presence of an adjacent hole on the values of the first-neighbor interactions. The dependence of JNN and tNN on the position of neighbor hole~s! has been rationalized from the two-band model and checked from a series of additional ab initio calculations. An extended t-J model Hamiltonian has been proposed on the basis of these results. It is argued that the hereproposed three-body effects may play a role in the charge/spin separation observed in these compounds, that is, in the formation and dynamic of stripes