Stripe formation in repulsive 4-leg Hubbard ladder: Directly-extended DMRG studies

In order to study the ground state of the Hubbard model from a slightly doped region to an over-doped one, we directly apply the density renormalization group method to 4-leg × 20-ladder repulsive Hubbard model and calculate hole distribution profiles with changing the on-site repulsion U/t from 0 to 15 and the doping ratio from 0.025 to 0.250. The calculation results in the underdoped range reveal that various stripe structures formed by doped holes merge or separate depending on U/t and the doping ratio. We suggest that these rich features are relevant to modulated hole distributions as experimentally observed in underdoped high-Tc superconductors.