Observation of Josephson plasma in orientation and carrier-controlled YBa2Cu3O7-δ films

In-plane c-axis aligned YBa2Cu3O7-delta(1 1 0) has been deposited on SrTiO3(1 1 0) substrates by pulsed laser deposition using a self-template technique. The films were highly crystalline. The oxygen deficiencies of the films were adjusted by controlling the oxygen partial pressure during in situ annealing. We carried out c-axis far-infrared reflectivity measurement on these films and it was found that in the normal state the carriers are confined in the Cu-O planes and their transport along c-axis is incoherent. A pseudogap developed in the normal state at temperatures well above the superconducting transition temperature, T-c, and it persisted in the superconducting state. When the temperature decreased below T-c, coherence is built up for carrier transport along the c-axis and a reflectivity edge associated with Josephson plasma was observed at around 110 cm(-1) (similar to 14 meV). (C) 2001 Elsevier Science B.V. All rights reserved.