Investigation of charge stripe formation in an extended t-J model

We consider a possible mechanism of the charge stripes in the high-T-c cuprates, based on some additional interactions in the two-dimensional t-J model; the next-nearest-neighbour and/or four-spin (ring) exchange interactions. The many-hole correlation functions obtained by numerical exact diagonalization of a finite-cluster t-J model including the correction terms indicate the realization of the mechanism and give some preliminary phase diagrams. A realistic combination of these additional terms is also studied.