Photoexcitation and oxygen ordering in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathit{x}}$ films

We report on the photoinduced enhancement of the critical temperature δ${\mathit{T}}_{\mathit{c}}$ and the in-plane conductivity δ${\mathrm{\sigma }}_{\mathit{a}\mathit{b}}$ measured in a c-axis-oriented ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{\mathit{x}}$ film as a function of oxygen concentration (6.4≤x≤7). Both δ${\mathit{T}}_{\mathit{c}}$ and δ${\mathrm{\sigma }}_{\mathit{a}\mathit{b}}$ decrease with the oxygen content, display a plateaulike behavior for 6.6≤x≤6.75, and become zero at x=7. This dependence of δ${\mathit{T}}_{\mathit{c}}$ on x is similar to that observed for the ${\mathit{T}}_{\mathit{c}}$ enhancement due to ordering effects in oxygen-deficient ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{\mathit{x}}$ single crystals. We propose that the persistent photoinduced changes in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{\mathit{x}}$ films are due to photoassisted oxygen ordering.