Breakdown of the Luttinger sum rule at the Mott-Hubbard transition in the one-dimensional t1-t2 Hubbard model

We investigate the momentum distribution function near the Mott-Hubbard transition in the one-dimensional t(1)-t(2) Hubbard model (the zigzag Hubbard chain) with the density matrix renormalization group technique. We show that for strong interactions the Mott-Hubbard transition occurs between the metallic phase and an insulating dimerized phase with incommensurate spin excitations, suggesting a decoupling of magnetic and charge excitations not present in weak coupling. We illustrate the signatures for the Mott-Hubbard transition and the commensurate-incommensurate transition in the insulating spin-gaped state in their respective ground-state momentum distribution functions.