  We investigate the momentum distribution function near the Mott-Hubbard
transition in the one-dimensional t1-t2 Hubbard model (the zig-zag 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-gapped state in their respective ground-state momentum distribution
functions.
