Stripe orientation in an anisotropic t − J model

The tilt pattern of the CuO6 octahedra in the low-temperature tetragonal ~LTT! phase of the cuprate superconductors leads to planar anisotropies for the exchange coupling and hopping integrals. Here, we show that these anisotropies provide a possible structural mechanism for the orientation of stripes. A t x-t y-J x-J y model thus serves as an effective Hamiltonian to describe stripe formation and orientation in LTT-phase cuprates. Early Hartree-Fock calculations 1 found evidence for domain-wall formation in doped two-dimensional ~2D! Hubbard and t-J models. In these calculations the domain walls contained one hole per unit cell and separated p-phase-shifted antiferromagnetic ~AF! regions. Subsequent density-matrix-renormalization-group ~DMRG! calculations 2 also found hole-domain walls separating p-phase-shifted AF regions, but in these calculations the linear filling of the horizontal ~or vertical! domain walls corresponded to one hole per two unit cells of the wall. In these calculations, domainwall formation originates as a compromise in the inherent competition between the kinetic and exchange energies which arises when holes are added to a Mott antiferromagnetic insulator. In the parameter regime where horizontal or vertical stripes formed, these fourfold rotationally invariant models did not distinguish between the two orientations. Here we wish to discuss a possible electronic mechanism for