  Nano-scaled substrate surface roughness is shown to strongly influence the
critical current density Jc in YBCO films made by pulse-laser-deposition on the
crystalline LaAlO3 substrates consisting of two separate twin-free and
twin-rich regions. The nano-scaled corrugated surface was created in the
twin-rich region during the deposition process. Using magneto-optical imaging
techniques coupled with optical and atomic force microscopy, we observed an
enhanced flux pinning in the YBCO films in the twin-rich region, resulted in
\~30% increase in Jc, which was unambiguously confirmed by the direct transport
measurement.
