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, at 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 intersite Coulomb interaction and quantum/thermal fluctuations. The optical spectra in CO_1/3 show multiple components and their low-energy weights survive even below the ordering temperature (T_CO). The changes in the dynamical charge correlation below T_CO in CO_1/3 are weakly momentumdependent, in sharp contrast to those in CO_1/2. These characteristic dynamics in CO_1/3 are attributable to charge frustration effects and reproduce some aspects of the recent experimental optical and X-ray scattering spectra.