SYSTEMATIC EVOLUTION OF ELECTRON LOCALIZATION IN BI2SR2CUOY

The electronic transport properties in Bi2Sr2CuOy crystals have been i nvestigated with the focus on the localized behaviours at low temperat ure. It is found that in the passage of transition from metallic to in sulating states the samples first show two-dimensional weak-localizati on behaviour, and cross over to the variable-range hopping conduction corresponding to the strong-localization regime. We analyse the experi mental results and suggest that the metal-insulator transition is caus ed by the effects of both disorder in the lattice and electron correla tions.