Photoinduced oxygen reordering in ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$ single crystals

Temporal changes in Raman-scattering spectra of oxygen-deficient ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-x}$ single crystals have been studied under exposure of polarized laser light with very low power of the order of 1 ${\mathrm{W}/\mathrm{c}\mathrm{m}}^2$. Intensities of the additional lines, which appear in Raman spectra because of the imperfectness of oxygen chains, have been found to depend not only on the oxygen content but also on the time elapsed after the beginning of the laser irradiation during Raman measurement. This temporal change obeys the exponential-decay law well with the characteristic time remarkably depending on the temperature. We attribute the observed phenomenon to a metastability of the oxygen ordering in imperfect chains.