LU CFI Zinātniskais seminārs (29.04.2013)

Oxygen chain fragments are known to appear at the insulator-to-superconductor transition in YBa₂Cu₃O₆+y. However, the self-organization and the size distribution of oxygen chain fragments are not known. Here, we seek to fill this gap, using scanning micro-x-ray diffraction, which is an imaging method based on advances in focusing a synchrotron radiation beam. This approach allows us to probe both real-space and k-space of high-quality YBa₂Cu₃O_6.33 single crystals with T_c = 7 K. We report compelling evidence for nanoscale striped puddles, with Ortho-II structure, made of chain fragments in the basal Cu(1) plane with local oxygen concentration y = 0.5. The size of the Ortho-II puddles spans a range between 2 and 9 nm. The real-space imaging of Ortho-II puddles granular network shows that superconductivity, at a low hole-doping regime, occurs in a network of nanoscale oxygen ordered patches, interspersed with oxygen depleted regions. The manipulation by thermal treatments of the striped Ortho-II puddles has been investigated focusing on the spontaneous symmetry breaking near the order-to-disorder phase transition at T₀ = 350 K.