Origin of charge density wave in the coupled spin ladders in Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$

TL;DR

This study develops a multiband charge transfer model for coupled spin ladders in Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$, revealing how electronic interactions and interladder couplings influence charge density wave formation and periodicity.

Contribution

It introduces a detailed multiband model and demonstrates how electronic interactions and interladder couplings determine CDW stability and periodicity.

Findings

Charge density wave stability depends on doping and interladder interactions.

Purely electronic many-body interactions can stabilize CDW in a single ladder.

Interladder interactions favor odd periodicity CDWs, disfavoring even ones.

Abstract

We formulate a d-p multiband charge transfer model for Cu$_2$O$_5$ coupled spin ladders, relevant for Cu$_2$O$_3$ plane of Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$, and solve it using Hartree-Fock approximation. The results explain that (i) the charge density wave (CDW) with its periodicity dependent on doping is stabilized by purely electronic many-body interactions in a single spin ladder and (ii) the inclusion of the interladder interactions favors (disfavors) the stability of the CDW with odd (even) periodicity, respectively. This stays in agreement with recent experimental results and suggests the structure of the minimal microscopic model which should be considered in future more sophisticated studies.