Cluster variation method investigation of photoinduced charge transfer in YBa2Cu3O6+x material

Abstract

According to the charge transfer model of Kudinov et a]. the photoinduced enhancement of conductivity in YBa2Cu3O6+x material can be explained by the photoexcitation of electron-hole pairs, and the subsequent transfer of electrons to the oxygen deficient CuOx planes where they become trapped in the CuO chain fragments, while the holes remain free in the superconducting CUO2 planes contributing to the superconducting current. In this paper we have employed the numerical cluster variation method (CVM) and the recently established relation between chain probability distribution p(n) and the average chain length n(av), to calculate the number of electrons being captured in the unoccupied p orbitals of O- ions incorporated in the CuO chains, thus producing the free holes in the CUO2 planes. Our results support the standing that several processes make contribution to the effects of persistent photoconductivity and photoinduced superconductivity. (C) 2007 Elsevier B.V. All rights reserved.