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

摘要

A series of accurate ab initio calculations on Cu_pO-q finite clusters,properly embedded on the Madelung potential of the infinite lattice, have beenperformed in order to determine the local effective interactions in the CuO_2planes of La_{2-x}Sr_xCuO_4 compounds. The values of the first-neighborinteractions, magnetic coupling (J_{NN}=125 meV) and hopping integral(t_{NN}=-555 meV), have been confirmed. Important additional effects areevidenced, concerning essentially the second-neighbor hopping integralt_{NNN}=+110meV, the displacement of a singlet toward an adjacent colinearhole, h_{SD}^{abc}=-80 meV, a non-negligible hole-hole repulsionV_{NN}-V_{NNN}=0.8 eV and a strong anisotropic effect of the presence of anadjacent hole on the values of the first-neighbor interactions. The dependenceof J_{NN} and t_{NN} on the position of neighbor hole(s) has been rationalizedfrom the two-band model and checked from a series of additional ab initiocalculations. An extended t-J model Hamiltonian has been proposed on the basisof these results. It is argued that the here-proposed three-body effects mayplay a role in the charge/spin separation observed in these compounds, that is,in the formation and dynamic of stripes.