Observation of two-dimensional layer-by-layer growth of NdBa ₂ Cu ₃ O 7 − δ epitaxial films with high T C on SrTiO ₃ and LaAlO ₃ by pulsed-laser deposition

We report the surface characteristics and superconducting properties of epitaxial NdBa 2 Cu 3 O 7 − δ thin films grown on (100) SrTiO 3 and (100) LaAlO 3 substrates by pulsed-laser deposition technique from a stoichiometric NdBa 2 Cu 3 O 7 − δ target. The NdBa 2 Cu 3 O 7 − δ films grown under the newly optimised deposition parameters showed a clear two-dimensional nucleation followed by a layer-by-layer growth resulting in a very smooth surface with typical root-mean-square surface roughness as low as 0.5 nm for a 2 μm × 2 μm area. The films showed high crystallinity and excellent in-plane epitaxy. Also the films showed good metallicity and gave a zero resistance superconducting transition of 92 K with a narrow transition width of ∼ 0.5 K. Even the films with thickness above 400 nm grew in the same growth mode indicating that there was no change in the growth mode of NdBa 2 Cu 3 O 7 − δ films with increasing thickness under the newly optimised deposition condition. The realization of reproducible growth of NdBa 2 Cu 3 O 7 − δ films with high T C and smooth surface on LaAlO 3 will have tremendous application in superconducting microwave devices.