Strain amplification of the 4kF chain instability in Sr14Cu24O41

We used resonant soft x-ray scattering to study the chain ordering in Sr14Cu24O41 (SCO). We observed, for the first time, both the chain and ladder orders in SCO with the same probe. We found that the chain modulation in SCO is incommensurate with wave vector Lc=0.318, is strongly temperature (T) dependent, and is accompanied by a substantial hole modulation. By contrast, the chain modulation in a hole-depleted control sample La6Ca8Cu24O41 was commensurate (Lc=0.3), T independent, and purely structural. We conclude that the chain charge order in SCO is a 4kF charge density wave stabilized by the misfit strain between the ladder and chain substructures.