High energy x-ray diffraction from high Tc superconductors

High-energy x-ray diffraction revealed short-range ordered 4-unit-cell modulation, q0=(1/4,0,0), in optimally doped YBCO superconductor (Fig. a-b). Model calculations show that Ba, Cu, and O atoms are displaced along the shorter Cu-Cu bond direction with no displacements along the chains (Fig. c). The displacement pattern is consistent with oxygen-vacancy ordering with the same periodicity. The modulated regions induce strains in the host lattice yielding “bow-tie” shape Huang diffuse scattering near Bragg points (Fig. d), which is masked at room temperature by thermal diffuse scattering (Fig. (e)). Fig. (a-d) are from data collected at ~7 K. [Phys. Rev. Lett. 93, 157008 (2004)].

Local Contact: Zahir Islam ( zahir@aps.anl.gov)


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