Enhancement of transport critical current density of epitaxial Nb film by lithography

The critical current density, JC, of a superconductor is controlled by the pinning interaction between the flux line lattice and pinning centers. Artificial flux pinning centers are necessary for high-TC superconductors, because JC decreases markedly when a magnetic field of a few Tesla is applied at the temperature of liquid nitrogen. Here, we discuss the effects of groove-shaped artificial pinning centers introduced by microlithography. Superconducting Nb film was deposited epitaxially on Al2O3(1 1 0 2) substrates and grooves with a period of 4-μm were introduced. The micro-fabricated film had about 2-fold greater transport JC = 4.1 × 109 A/m2 as compared with the value of JC = 2.1 × 109 A/m2 of the standard film at 4.2 K, 0.1 T. This JC enhancement was observed over a wide temperature range of 4.2-9.0 K.