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

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.