Periodic hole structure in a spin-chain ladder material Sr₁₄Cu₂₄O₄₁

High-energy synchrotron x-ray diffraction measurements were carried out on a single crystal of Sr₁₄Cu₂₄O₄₁, which had been reported to have different magnetic and structural correlations, in order to investigate the origin of this discrepancy more precisely. At low temperature, we observed weak superlattice peaks at Q=(0,0,2n±1/5)_c, while nothing was found at Q=(0,0,2n±1/4)_c, which was reported in a previous x-ray work by Cox et al. [Phys. Rev. B 57, 10 750 (1998)]. Therefore, the lattice distortion has not 4 but 5 times the periodicity of the chain structure along c (‖ chain axis) direction. These satellite peaks decreased in intensity with increasing temperature. These observations were interpreted properly in terms of a hole ordering model involving the dimerized state of two Cu²⁺ ions and a Cu³⁺ ion on a Zhang-Rice singlet site in the CuO₂ chains. These features were clearly observed by using high-energy x rays (E_i≃53.789 keV), while the superlattice peak intensity varied drastically with very little sample surface treatment in the case of low-energy x-ray experiments (E_i≃15.498 keV).