J. Phys. IV France 114 (2004) 29
DOI: 10.1051/jp4:2004114005

Quantum effects on charge order

H. Seo^{1, 1}, M. Ogata² and M. Kuwabara<sup>3

1</sup>  Correlated Electron Research Center (CERC), AIST Tsukuba Central 4, Ibaraki 305-8562, Japan; Domestic Research Fellow, JSPS, Tokyo 102-8471, Japan
²  Department of Physics, University of Tokyo, Tokyo 113-0033, Japan
³  The Institute of Pure and Applied Physics, Tokyo 105-0004, Japan

Abstract
Charge ordering in strongly correlated 1/4-filled systems, such as charge transfer organic conductors and transition metal oxides, is discussed from a theoretical point of view. Strong electron-electron Coulomb interaction especially that between neighboring molecules induces Wigner crystal-type charge order, which competes with another insulating state due to strong correlation in these systems, i.e., the dimer Mott insulating state. Based on such idea, new aspects of the charge ordering phenomenon are pointed out, where full quantum mechanical treatments are required. One case is the interplay between electron-phonon interaction leading to a novel co-existence of charge order and spin-Peierls lattice distortion, and the other is the effect of geometrical frustration resulting in a quantum melting of the charge order. Key words. charge order, strongly correlated electron system, electron-phonon interaction, geometrical frustration.

© EDP Sciences 2004