Charge fluctuations in geometrically frustrated charge ordering system

Abstract

Effects of geometrical frustration in low-dimensional charge ordering systems are theoretically studied, mainly focusing on dynamical properties. We treat extended Hubbard models at quarter-filling, where the frustration arises from competing charge ordered patterns favored by different intersite Coulomb interactions, which are effective models for various charge transfer-type molecular conductors and transition metal oxides. Two different lattice structures are considered: (a) one-dimensional chain with intersite Coulomb interaction of nearest neighbor V 1 and that of next-nearest neighbor V 2, and (b) two-dimensional square lattice with V 1along the squares and V 2 along one of the diagonals. From previous studies, charge ordered insulating states are known to be unstable in the frustrated region, i.e., V 1 ≃2 V 2 for case (a) and V 1 ≃ V 2 for case (b), resulting in a robust metallic phase even when the interaction strengths are strong. By applying the Lanczos exact diagonalization to finite-size clusters, we have found that fluctuations of different charge order patterns exist in the frustration-induced metallic phase, showing up as characteristic low energy modes in dynamical correlation functions. Comparison of such features between the two models is discussed, whose difference will be ascribed to the dimensionality effect. We also point out incommensurate correlation in the charge sector due to the frustration, found in one-dimensional clusters