  In strongly correlated electron systems, the emergence of states in the Mott
gap in the single-particle spectrum following the doping of the Mott insulator
is a remarkable feature that cannot be explained in a conventional rigid-band
picture. Here, based on an analysis of the quantum numbers and the overlaps of
relevant states, as well as through a demonstration using the ladder and
bilayer t-J models, it is shown that in a continuous Mott transition due to
hole doping, the magnetically excited states of the Mott insulator generally
emerge in the electron-addition spectrum with the dispersion relation shifted
by the Fermi momentum in the momentum region where the lower Hubbard band is
not completely filled. This implies that the dispersion relation of a
free-electron-like mode in the electron-addition spectrum eventually transforms
into essentially the momentum-shifted magnetic dispersion relation of the Mott
insulator, while its spectral weight gradually disappears toward the Mott
transition. This feature reflects the spin-charge separation of the Mott
insulator.
