Evidence for Photoinduced Hole Coupling in BaTiO3:Co

A possible photoinduced correlation mechanism in BaTiO 3 : Co is described. The underlying microscopic process is a local hole photoinjection at a Co 3+ site close to a preexisting metastable hole, The Jahn-Teller field at the Co 2+ site transfers this pair of holes in the next cell along the rhombic direction [111] before normal polaronic or band conduction. The spatial extension of this correlation depends on a characteristic «delocalization» length. This unstable conductive state appears to be possibly frozen in a permanent way below T c