Sliding density-wave in Sr14Cu24O41 ladder compounds
26 July 2002
Sr14Cu24O41 ladder compounds contain linear fragments of copper oxide planes that are responsible for high-temperature superconductivity in two-dimensional cuprates. The undoped spin 1/2 two-leg ladders have short-range magnetic order and a spin gap in contrast to the two-dimensional antiferromagnetic cuprates. Holes doped into these ladders pair and superconduct at high doping concentrations, while insulators are known to result from low hole concentrations. The competition between insulating states and superconductive pairing has emerged as a key feature of the high-Tc problem, but the character of the insulating states has remained elusive. Here, using transport and Raman scattering data, we identify the insu- lating state of self-doped two-leg spin ladders of Sr14Cu24O41 as a weakly pinned, sliding density wave. This collective density- wave state exhibits a giant dielectric response, non-linear conductivity, and persists to well above room temperature.