  Within the framework of the fermion-spin theory, the charge transport in the
doped Mott insulators on a honeycomb lattice is studied by taking into account
the pseudogap effect. It is shown that the conductivity spectrum in the
low-doped regime is separated by the pseudogap into a low-energy non-Drude peak
followed by a broad midinfrared band. However, the decrease of the pseudogap
with the increase of doping leads to a shift of the position of the midinfrared
band towards to the low-energy non-Drude peak, and then the low-energy Drude
behavior recovers in the high-doped regime. The combined results of both the
doped honeycomb-lattice and square-lattice Mott insulators indicate that the
two-component conductivity induced by the pseudogap is a universal feature in
the doped Mott insulators.
