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Charge Dynamics in a Correlated Fermion System on a Geometrically Frustrated Lattice

Charge dynamics in an interacting fermionic model on a geometrically frustrated lattice are examined. We analyze a spinless fermion model on a paired triangular lattice, an electronic model for layered iron oxides, in zero and finite temperatures by the exact diagonalization methods. We focus on the two charge ordered (CO) phases, termed CO_1/2 and CO_1/3, which, respectively, are realized by the inter-site Coulomb interaction and the quantum/thermal fluctuations. The optical spectra in CO_1/3 show multiple components and their low-energy weights are survived even below the ordering temperature (T_CO). Changes of the dynamical charge correlation below T_CO in CO_1/3 are weakly momentum dependent, in sharply contrast to CO_1/2. These characteristic dynamics in CO_1/3 are attributable to the charge frustration effects, and reproduce some aspects of the recent experimental optical and x-ray scattering spectra.