Charge Order and Superconductivity in Two-Dimensional Triangular Lattice at n=2⁄3

Abstract

To investigate the possibility of charge order and superconductivity in a doped two-dimensional triangular lattice, we study an extended Hubbard model with the variational Monte Carlo method. At n=2⁄3, a commensurate filling for a triangular lattice, it is shown that the nearest-neighbor Coulomb interaction V induces honeycomb-type charge order and antiferromagnetic spin order at U\\gtrsim10t. We also discuss the possibility of superconductivity induced by charge fluctuation and the relation to the superconductivity in Na_0.35CoO₂·1.3H₂O and θ-type organic condoctors.