We studied the photoinduced metastable states in oxygen-deficient YBa2Cu3Ox (Y123) (x = 6.35-6.87). The states are identified by the intensity dependences of CuO-chain resonance on photo irradiation and temperature. Below room temperature (RT) the CuO-chain resonance can be completely suppressed by irradiation with visible light polarized along the CuO chains, indicating photo-assisted oxygen ordering. Above RT, the resonance intensity returns and saturates at T > 100°C. This behavior exactly reflects the temperature dependence of chain oxygen ordering in the same crystals observed by hard X-ray diffraction. The stability of the photo-induced state is in agreement with reported persistent photo-induced superconductivity effects.
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