Charge Fluctuations in Geometrically Frustrated Charge Ordering System

TL;DR

This paper investigates how geometrical frustration affects charge fluctuations and dynamical properties in low-dimensional extended Hubbard models, revealing persistent charge pattern fluctuations and incommensurate correlations in frustrated metallic phases.

Contribution

It provides a comparative analysis of charge fluctuations in 1D and 2D frustrated systems using exact diagonalization, highlighting the role of dimensionality.

Findings

Charge fluctuations persist in the frustrated metallic phase.

Low energy modes indicate competing charge order patterns.

Incommensurate charge correlations are observed in 1D clusters.

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_1 along 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 \simeq 2V_2 for case (a) and V_1 \simeq V_2 for case (b), resulting in a robust metallic phase even when the interaction strenghs 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 are 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.