Coexistence of charge density wave and spin-Peierls orders in quarter-filled quasi-one dimensional correlated electron systems

TL;DR

This study investigates how charge density waves and spin-Peierls orders coexist in quarter-filled quasi-one-dimensional systems, revealing that moderate couplings can stabilize multiple intertwined orders, with implications for materials like NaV2O5.

Contribution

It demonstrates the coexistence of charge density waves, bond order waves, and spin-Peierls orders in coupled ladder and chain systems using numerical models, highlighting the effects of various interactions.

Findings

Coexistence of multiple orders in ladder and chain systems.

Holstein coupling stabilizes zig-zag patterns and modulations.

Charge ordering enhances spin-Peierls instability in chains.

Abstract

Charge and spin-Peierls instabilities in quarter-filled (n=1/2) compounds consisting of coupled ladders and/or zig-zag chains are investigated. Hubbard and t-J models including local Holstein and/or Peierls couplings to the lattice are studied by numerical techniques. Next nearest neighbor hopping and magnetic exchange, and short-range Coulomb interactions are also considered. We show that, generically, these systems undergo instabilities towards the formation of Charge Density Waves, Bond Order Waves and (generalized) spin-Peierls modulated structures. Moderate electron-electron and electron-lattice couplings can lead to a coexistence of these three types of orders. In the ladder, a zig-zag pattern is stabilized by the Holstein coupling and the nearest-neighbor Coulomb repulsion. In the case of an isolated chain, bond-centered and site-centered 2k_F and 4k_F modulations are induced by the local Holstein coupling. In addition, we show that, in contrast to the ladders, a small charge ordering in the chains, strongly enhances the spin-Peierls instability. Our results are applied to the NaV_2O_5 compound (trellis lattice) and various phases with coexisting charge disproportionation and spin-Peierls order are proposed and discussed in the context of recent experiments. The role of the long-range Coulomb potential is also outlined.