Electronic structure of partially-doped insulating cuprates: photo doping studies

Summary form only given. A series of photodoping experiments in partially doped insulating cuprates were carried out in our laboratory recently. By means of transient photoexcitation, we have demonstrated photoinduced metal-insulator (M-I) transitions in 123 and 214 systems. In this presentation, we summarize the experimental effects and discuss their physical implications. The existence of a Fermi-glass insulating state in insulating cuprates is explored. The localized electronic states near the Fermi energy (E/sub F/) are characterized through transport, steady state photoconductivity and time resolved transient photodoping experiments (with subnanosecond time resolution). The experimental results indicate an Anderson-type metal-insulator transition in the doped cuprates; i.e., the transition from metal to insulator is dominated by disorder-induced localization. The E/sub F/ can be shifted across the mobility edge either by increasing the doping level or by transient photoexcitation at high pump intensities, thereby causing the M-I transition. Although the photo-carriers are generated homogeneously, the data suggest electronic phase separation into metallic droplets. The temperature dependence of the photoinduced conductivity implies that these droplets become superconducting below the intrinsic transition temperature observed in the heavily doped metallic regime.