Microstructure and properties of groove-shaped artificial pinning centers introduced by microfabrication

Effective flux pinning centers are required for the development of practical superconductors in order to achieve high critical current density. In the case of metallic superconductors, a drawing process introduces artificial pinning centers in metallic superconductors. However, artificial pinning centers cannot be introduced into high-Tc superconductors through the drawing process because these superconductors are brittle. We consider the microfabrication technique, instead of the drawing process, in order to introduce artificial pinning centers into the superconductors. Groove-shaped artificial pinning centers are introduced into a 0.5 μm thick evaporated Nb film on a sapphire substrate by photolithography. The groove-shaped pattern with a spacing of 4 μm was introduced by etching on a 0.9 × 0.9 mm region of the Nb film. Nb films with varying groove depths were prepared, and the groove depth dependence on critical current density was investigated for the width of the hysteresis curve of the magnetic moment. The hysteresis curves of the specimens with grooves were measured with a SQUID magnetometer. The width of the hysteresis curve decreases with an increasing groove depth for over 70% of the film thickness.