Ground-state phases of the extended Hubbard model

Longer-range interactions often play important roles in shaping the physics of strongly correlated systems. In many cases they can qualitatively alter the underlying ground state. We investigate an extended repulsive Hubbard model with near-neighbor interaction $V$ in addition to the usual on-site repulsion $U$, using a combination of state-of-the-art numerical methods, the density matrix renormalization group (DMRG) and constrained-path auxiliary-field quantum Monte Carlo (CP-AFQMC). We investigate the ground state phase diagram. As $V/U$ is increased, a number of novel phases emerge, beyond the physics of the usual Hubbard model. For an unpolarized system (fixed $N_\uparrow=N_\downarrow$, as in, e.g., cold atoms experiments), the system exhibits alternating polarized spin stripes coexisting with a charge density wave (CDW). When the spin degree of freedom is allowed to vary, the ground state is characterized by a ferrimagnetic order. We further explore the effect of next-nearest-neighbor hopping $t^\prime$, which is found to modify the stripe periodicity without significantly shifting the critical ratio $V_c/U$.