Effects of epitaxial strain on the growth mechanism inYBa2Cu3O7−xthin films inYBa2Cu3O7−x/PrBa2Cu3O7superlattices

Abstract

We report on the growth mechanism of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}.$ Our study is based on an analysis of ultrathin ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$ (YBCO) layers in c-axis-oriented ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}/{\mathrm{PrBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ superlattices. We have found that the release of epitaxial strain in very thin YBCO layers triggers a change in the dimensionality of the growth mode. Ultrathin epitaxially strained YBCO layers with thickness below 3 unit cells grow in a block-by-block two-dimensional mode that is coherent over large lateral distances. Meanwhile, when the thickness increases and the strain relaxes, layer growth turns three-dimensional, resulting in rougher layers and interfaces.