<i>a</i>-axis YBa₂Cu₃O_7-<i>x</i>/PrBa₂Cu₃O_7-<i>x</i>/YBa₂Cu₃O_7-<i>x</i> trilayers with improved interface and surface roughness

We demonstrate a-axis YBa₂Cu₃O_7-x/PrBa₂Cu₃O_7-x/YBa₂Cu₃O_7-x trilayers grown on (100) LaAlO₃ substrates with improved interface smoothness. [1] The trilayers are synthesized by ozone-assisted molecular-beam epitaxy. The thickness of the PrBa₂Cu₃O_7-x layer is held constant at 8 nm and the thickness of the YBa₂Cu₃O_7-x layers is varied from 24 nm to 100 nm. X-ray diffraction measurements show all trilayers to have >95% a-axis content. The rms roughness of the thinnest trilayer is <0.7 nm and this roughness increases with the thickness of the YBa₂Cu₃O_7-x layers. The thickness of the YBa₂Cu₃O_7-x layers also affects the transport properties: while all samples exhibit an onset of the superconducting transition at and above 85 K, the thinner samples show wider transition widths, ΔT_c. High-resolution scanning transmission electron microscopy reveals coherent and chemically sharp interfaces, and that growth begins with a cubic (Y,Ba)CuO_3-x perovskite phase that transforms into a-axis oriented YBa₂Cu₃O_7-x as the substrate temperature is ramped up.

[1] Y. E. Suyolcu, J. Sun, B. H. Goodge, J. Park, J. Schubert, L. F. Kourkoutis, and D. G. Schlom, arXiv:2010.12624 (2020)