Spin dynamics and sliding density wave in Sr Cu O ladders

Sr Cu O ladder compounds contain linear frag ments of copper oxide planes In contrast to the two dimensional antiferromagnetic cuprates the spin two leg ladders have short range magnetic order and a spin gap Holes doped into these ladders pair and superconduct at high doping concentrations while insulators are known to result from low hole concen trations 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 insulating state of self doped two leg spin ladders of Sr Cu O as a weakly pinned sliding density wave This collective density wave state exhibits a giant di electric response non linear conductivity and persists to well above room temperature Our results have quantitative parallels with sliding density wave transport phenomena observed in estab