Charge-ordered manganites of composition $\rm Pr_{ 1-x}(Ca_{ 1-y}Sr_{ y})_{ x}MnO_3$ exhibit persistent photoconductivity upon exposure to x-rays. This is not always accompanied by a significant increase in the { \it number} of conduction electrons as predicted by conventional models of persistent photoconductivity. An analysis of the x-ray diffraction patterns and current-voltage characteristics shows that x-ray illumination results in a microscopically phase separated state in which charge-ordered insulating regions provide barriers against charge transport between metallic clusters. The dominant effect of x-ray illumination is to enhance the electron { \it mobility} by lowering or removing these barriers. A mechanism based on magnetic degrees of freedom is proposed.
Categories: cond-mat.mtrl-sci cond-mat.str-el