Superconductivity in the three-fold charge-ordered metal of the triangular-lattice extended Hubbard model

The quarter-filling extended Hubbard model on the triangular lattice is studied to explore pairing instability in the three-fold charge-ordered (CO) metal. We derive a second-order strong-coupling effective Hamiltonian of doped carriers into the three-fold CO insulator at electron density of n = 2/3, and then study the f- and d(xy)-wave superconductivities down to n = 1/2 by using the Bardeen-Cooper-Schrieffer mean-field approximation. It is found that the triplet f-wave pairing is more stable than the d(xy)-wave one. We also discuss that this coexisting state of the charge ordering and superconductivity is possible to have critical temperature T-c similar to 0.01t.