Epitaxial Y1Ba2Cu3O7 thin films on CeO2 buffer layers on sapphire substrates

Pulsed laser deposition has been used to deposit Y1Ba2Cu3O7 layer on CeO2 buffer layers on (11_02) sapphire. Both layers are epitaxial with the 〈110〉 direction of the CeO2 layer aligned with the 〈2_021〉 direction of the sapphire substrate. The c-axis Y1Ba2Cu3O7 layer has its 〈100〉 direction alligned with the 〈110〉 direction of the CeO2. Cross-sectional transmission electron microscopy shows the epitaxy to be coherent and the interfaces to be abrupt at an atomic level. The best films have a critical current of 9 × 106 A/cm2 at 4.2 K and lower microwave surface resistance than copper at 77 K and at a frequency of 31 GHz.