Numerical study on the anisotropic triangular-lattice Hubbard model at quarter filling: Charge fluctuations with three-fold periodicity Original Research Article

We study the extended Hubbard model at quarter filling defined on the anisotropic triangular lattices. We use the density-matrix renormalization group (DMRG) method to determine the ground-state phase diagram and the dynamical DMRG and Lanczos exact-diagonalization methods to calculate the excitation spectra. We find that the charge fluctuation with the three-fold periodicity, as well as the vertical and diagonal charge stripes, appears in realistic parameter ranges. We also find that, in the charge excitation spectra, there appear the low-energy collective modes in the entire Brillouin zone, together with the low-energy Drude-like peak separated from the high-energy broad features in the optical conductivity spectra, indicating the presence of the anomalous charge excitations in the state with the three-fold charge fluctuations.