Defect mechanism of photoinduced superconductivity inYBa2Cu3O6+x

Although persistent photoconductivity and photoinduced superconductivity have been experimentally observed in oxygen-deficient and superconducting $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6+x}$, the mechanism which is responsible for these effects is still under debate. The possibility of a defect related mechanism in laser-deposited thin films of $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6+x}$ is studied using four-point resistivity and photoluminescence techniques. It is found that there is a correlation between the photoluminescence spectrum and the wavelength dependence of the photoinduced conductivity. Peaks in the luminescence spectrum change intensity upon initiation of the photoinduced state. These results support an oxygen vacancy defect model of photoinduced persistent conductivity and superconductivity in which the oxygen vacancies act as weakly luminescent $F$-centers under illumination.