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

In-plane c-axis aligned YBa2Cu3O7-δ(110) has been deposited on SrTiO3(110) 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, Tc, and it persisted in the superconducting state. When the temperature decreased below Tc, 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 (∼14 meV). © 2001 Elsevier Science B.V. All rights reserved.