  The Mott transition is usually considered as resulting from the divergence of
the effective mass of the quasiparticle in the Fermi-liquid theory; the
dispersion relation around the Fermi level is considered to become flat towards
the Mott transition. Here, to clarify the characterization of the Mott
transition under the assumption of a Fermi-liquid-like ground state, the
electron-addition excitation from the Gutzwiller wavefunction in the $t$-$J$
model is investigated on a chain, ladder, square lattice, and bilayer square
lattice in the single-mode approximation using a Monte Carlo method. The
numerical results demonstrate that an electronic mode that is continuously
deformed from a non-interacting band at zero electron density loses its
spectral weight and gradually disappears towards the Mott transition. It
exhibits essentially the magnetic dispersion relation shifted by the Fermi
momentum in the small-doping limit as indicated by recent studies for the
Hubbard and $t$-$J$ models, even if the ground state is assumed to be a
Fermi-liquid-like state exhibiting gradual disappearance of the quasiparticle
weight. This implies that, rather than as the divergence of the effective mass
or disappearance of the carrier density that is expected in conventional
single-particle pictures, the Mott transition can be better understood as
freezing of the charge degrees of freedom while the spin degrees of freedom
remain active, even if the ground state is like a Fermi liquid.
