  The tilt pattern of the CuO_6 octahedra in the 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.
