Persistent X-ray photoconductivity and percolation of metallic clusters in charge-ordered manganites

¹ Department of Physics, Princeton University, Princeton - NJ 08544, USA
² Max-Planck-Institut für Festkörperforschung - D-70569 Stuttgart, Germany
³ Department of Physics, Brookhaven National Laboratory - Upton, NY 11973, USA
⁴ Joint Research Center for Atom Technology (JRCAT), Tsukuba - Ibaraki 305, Japan
⁵ Department of Applied Physics, University of Tokyo - Tokyo 113, Japan

Received: 8 March 1999
Accepted: 23 April 1999

Abstract

Charge-ordered manganites of composition exhibit persistent photoconductivity upon exposure to X-rays. This is not always accompanied by a significant increase in the 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 mobility by lowering or removing these barriers. A mechanism based on magnetic degrees of freedom is proposed.