Enhanced flux pinning in y Ba ₂ Cu ₃ O _7-δ films by nanoscaled substrate surface roughness

Nanoscaled substrate surface roughness is shown to strongly influence the critical current density (Jc) in Y Ba2 Cu3 O7-δ (YBCO) films made by pulsed-laser deposition on the crystalline LaAl O3 substrates consisting of two separate twin-free and twin-rich regions. The nanoscaled 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, we observed an enhanced flux pinning in the YBCO films in the twin-rich region, resulting in a ∼30% increase in Jc, which was unambiguously confirmed by the direct transport measurement.