Abstract
We demonstrate a-axis YBa2Cu3O7−x/PrBa2Cu3O7−x/YBa2Cu3O7−x trilayers grown on (100) LaAlO3 substrates with improved interface smoothness. The trilayers are synthesized by ozone-assisted molecular-beam epitaxy. The thickness of the PrBa2Cu3O7−x layer is held constant at 8 nm, and the thickness of the YBa2Cu3O7−x layers is varied from 24 nm to 100 nm. X-ray diffraction measurements show all trilayers to have >97% a-axis content. The rms roughness of the thinnest trilayer is <0.7 nm, and this roughness increases with the thickness of the YBa2Cu3O7−x layers. The thickness of the YBa2Cu3O7−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, ΔTc. High-resolution scanning transmission electron microscopy reveals coherent and chemically sharp interfaces and that growth begins with a cubic (Y,Ba)CuO3−x perovskite phase that transforms into a-axis oriented YBa2Cu3O7−x as the substrate temperature is ramped up.
Highlights
A more direct approach to fabricate high quality Josephson junctions (JJs)—one that involves pristine interfaces formed without breaking vacuum—is through the growth of YBa2Cu3O7−x films oriented with the a-axis perpendicular to the film surface (i.e., a-axis oriented films)
We demonstrate a-axis YBa2Cu3O7−x/PrBa2Cu3O7−x/YBa2Cu3O7−x trilayers grown on (100) LaAlO3 substrates with improved interface smoothness
High-resolution scanning transmission electron microscopy reveals coherent and chemically sharp interfaces and that growth begins with a cubic (Y,Ba)CuO3−x perovskite phase that transforms into a-axis oriented YBa2Cu3O7−x as the substrate temperature is ramped up
Summary
A more direct approach to fabricate high quality JJs—one that involves pristine interfaces formed without breaking vacuum—is through the growth of YBa2Cu3O7−x films oriented with the a-axis perpendicular to the film surface (i.e., a-axis oriented films). We demonstrate a-axis YBa2Cu3O7−x/PrBa2Cu3O7−x/YBa2Cu3O7−x trilayers grown on (100) LaAlO3 substrates with improved interface smoothness.
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