Structural modulations in $Sr_{14} Cu_{24} O_{41}$ and their relation to charge ordering

TL;DR

This study investigates the incommensurate structural modulations in Sr$_{14}$Cu$_{24}$O$_{41}$ using x-ray diffraction, revealing temperature-dependent modulation reflections linked to hole localization rather than a five-fold periodicity.

Contribution

The paper provides a detailed analysis of lattice modulations in Sr$_{14}$Cu$_{24}$O$_{41}$, challenging previous claims of five-fold periodicity and linking modulations to hole localization effects.

Findings

Higher order modulation reflections increase dramatically at low temperatures.

No structural phase transition observed between 10 K and room temperature.

Modulations are due to hole localization, not five-fold periodicity.

Abstract

Structural properties of the spin chain and ladder compound Sr$_{14}$Cu$_{24}$O$_{41}$ have been studied using diffraction with hard x-rays. Strong incommensurate modulation reflections are observed due to the lattice mismatch of the chain and ladder structure, respectively. While modulation reflections of low orders display only a weak temperature independence, higher orders dramatically increase in intensity when cooling the sample to 10 K. All observed modulation reflections are indexed within the super space group symmetry and no structural phase transition could be identified between 10 K and room temperature. We argue that these modulation reflections are not caused by a five-fold periodicity of the chain lattice, as claimed by Fukuda et al. Phys. Rev. B 66, 012104 (2002), but that holes localize in the potential given by the lattice modulation, which in turn gives rise to a further deformation of the lattice.