In situ resonant Raman scattering and reversible photoinduced structural change in YBa2Cu3O6+x

We report on bidirectional photoswitching associated with the CuO chains in oxygen-deficient YBa2Cu3O6+x single crystals. By varying the wavelength of light polarized along the CuO chains, the material can be reversibly switched between two metastable states characterized by the existence or absence of a specific Raman scattering resonance. A comparison of the spectral efficiencies for this photoswitching with analogous data for the persistent photoconductivity and photoconductivity quenching effects suggests that the two phenomena have the same microscopic origin. We argue that the effects are due to photoinduced CuO charge-transfer excitations, which destabilize chains of different length depending on wavelength, and promote the growth of thermally inaccessible oxygen ordering configurations.