a-axis YBa2Cu3O7-x/PrBa2Cu3O7-x/YBa2Cu3O7-x trilayers with subnanometer rms roughness

TL;DR

This study reports the fabrication of a-axis YBa2Cu3O7-x/PrBa2Cu3O7-x/YBa2Cu3O7-x trilayers with ultra-smooth interfaces on LaAlO3 substrates, analyzing how layer thickness influences surface roughness and superconducting properties.

Contribution

It introduces a method to produce high-quality a-axis oriented trilayers with subnanometer roughness using ozone-assisted molecular-beam epitaxy.

Findings

Roughness of trilayers is less than 0.7 nm for the thinnest samples.

Superconducting transition temperature is above 85 K for all samples.

Thinner layers exhibit wider superconducting transition widths.

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 >95% 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, {\Delta}Tc. 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.