Enhanced Flux Pinning in YBCO Films by Nano-Scaled Substrate Surface Roughness

Nano-scaled substrate surface roughness is shown to strongly influence the critical current density ($J_{c})$ in YBCO films, We prepared high quality c-axis oriented YBCO thin films by pulsed laser deposition on the single crystal LaAlO$_{3}$ substrates consisting of two separate twin-free and twin-rich regions. The nano-scaled corrugated substrate surface was created in the twin-rich region during the deposition process. Using magneto-optical imaging techniques coupled with optical and atomic force microscopy (AFM), we observed an enhanced flux pinning in the YBCO films in the twin-rich region, corresponding to $\sim $ 30{\%} increase in $J_{c}$. This result suggests that some nano-scaled substrate surface roughness may be beneficial for increasing $J_{c}$ in YBCO coated conductors.