A Model Study of the Low-Energy Charge Dynamics of NaV_2O_5

TL;DR

This study uses exact-diagonalization to analyze low-energy charge excitations in models relevant to NaV_2O_5, revealing collective modes driven by intersite Coulomb interactions and discussing implications for charge ordering and valence fluctuations.

Contribution

It introduces a detailed model study of charge dynamics in NaV_2O_5 using exact diagonalization, highlighting the role of intersite Coulomb repulsions in low-energy excitations.

Findings

Intersite Coulomb repulsions induce low-energy collective charge modes.

Internal charge degrees of freedom of pairs are crucial for excitations.

Implications for charge ordering and valence fluctuations in NaV_2O_5.

Abstract

An exact-diagonalization technique on small clusters is used to calculate the dynamical density correlation functions of the dimerized t-J chain and coupled anisotropic t-J ladders (trellis lattice) at quarter filling, i.e., the systems regarded as a network of pairs (dimers or rungs) of sites coupled weakly via the hopping and exchange interactions. We thereby demonstrate that the intersite Coulomb repulsions between the pairs induce a low-energy collective mode in the charge excitations of the systems where the internal charge degrees of freedom of the pairs play an essential role. Implications to the electronic states of NaV_2O_5, i.e., fluctuations of the valence state of V ions and phase transition as a charge ordering, are discussed.