Pulsed laser deposition of CeO₂ and Ce_1−xM_xO₂ (M = La, Zr): Application to insulating barrier in cuprate heterostructures

Abstract

SrTiO₃ had been often tentatively used as an insulating barrier for HT superconductor/insulator heterostructures. Unfortunately, the deposition of SrTiO₃ on the YBa₂Cu₃O₇ inverse interface results in a poor epitaxial regrowth producing a high roughness dislocated titanate layer. Taking into account the good matching with YBa₂Cu₃O₇ and LaAlO₃, CeO₂ and Ce_1−xM_xO₂ (M = La, Zr), epitaxial layers were grown by pulsed laser deposition on LaAlO₃ substrates and introduced into YBa₂Cu₃O₇ based heterostructures as insulating barrier. After adjusting the growth parameters from RHEED oscillations, epitaxial growth is achieved, the oxide crystal axes being rotated by 45° from those of the substrate. The surface roughness of 250 nm thick films is very low with a rms value lower than 0.5 nm over 1 μm². The YBa₂Cu₃O₇ layers of a YBa₂Cu₃O₇/CeO₂ /YBa₂Cu₃O₇ heterostructures grown using these optimized parameters show an independent resistive transition, when the thickness is larger than 25 nm, respectively at T_c1 = 89.6K and T_c2 = 91.4K.