  The kinetic features of holes (electrons) in the Hubbard model are studied
using a variational Monte Carlo method. In doped Mott insulators (U>U_co),
holes are classified, in the sense of conduction, into two categories: (i) The
holes appearing in doublon-holon pairs are localized, encourage singlet pair
formation, and gain the energy to induce a superconducting transition. (ii) The
doped holes become carriers, make the system itinerant (superconducting or
metallic), but lose the energy in the transition. These two roles are
distinguished in correlated superconductivity. This feature is common to
antiferromagnetic transitions at large U/t.
