Raman scattering experiments on oxygen deficient ${\mathrm{GdBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_x$ thin films ($x=6.53,$ 6.7, 6.8, and 6.93) as a function of photoexcitation and annealing induced oxygen disorder are presented. Raman lines, unambiguously assigned to copper and oxygen vibrations involving atoms at the end of Cu-O chains, are used as markers for the existence of short chain fragments. The dynamics of chain conjunction and fragmentation was monitored by the peak intensity dependences with photoexcitation time and annealing temperature. These results demonstrate the presence of photoassisted oxygen ordering in these high-$T_c$ superconductors, and give definitive support for its ultimate role in the phenomena of persistent photoconductivity and photoinduced superconductivity.

• Received 1 June 1998

DOI:https://doi.org/10.1103/PhysRevB.58.9433