Strain amplification of the 4k$_F$ chain charge instability in Sr$_{14}$Cu$_{24}$O$_{41}$

TL;DR

This study reveals that misfit strain amplifies the 4k_F charge density wave in Sr$_{14}$Cu$_{24}$O$_{41}$, providing new insights into charge order mechanisms in cuprates.

Contribution

It demonstrates that misfit strain enhances the 4k_F CDW in Sr$_{14}$Cu$_{24}$O$_{41}$, offering a novel explanation for charge order in this material.

Findings

Strain wave in SCO is temperature-dependent and correlates with hole modulation.

LCCO shows weaker, temperature-independent strain wave without hole modulation.

The observed wave vector matches the 4k_F instability of the chain.

Abstract

We have used resonant soft x-ray scattering (RSXS) to study the misfit strain in Sr$_{14}$Cu$_{24}$O$_{41}$ (SCO), a cuprate that contains both doped spin ladders and spin chains, as well as a "control" sample without holes, La$_{6}$Ca$_{8}$Cu$_{24}$O$_{41}$ (LCCO). The misfit strain wave in SCO is strongly temperature (T)-dependent and is accompanied by a substantial hole modulation. In LCCO the strain wave is weaker, shows no hole modulation, and is T-independent. The observed strain wave vector, $L_c=0.318$, is close to the 4k$_F$ instability of the chain. Our results indicate that the chain charge order observed in SCO by several groups is a 4k$_F$ charge density wave (CDW) amplified by the misfit strain in this material. This demonstrates a new mechanism for CDW formation in condensed matter and resolves several contraversies over the transport properties of SCO.