Preparation of Narrowed ${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{7-{\rm x}}$ Nanobridges Down to 30 nm With Reduced Degradation

We have established the new method of fabricating high-J_c YBa₂Cu₃O_7-x (YBCO) nanobridges with high reproducibility. Nanobridges ranging in 30-400 nm wide were formed by using electron beam lithography. An ultra thin film of 2-3 nm-thick insulative YBCO was deposited after nanobridge formation for recovering the damaged films occurred in the process. The critical current density J_c was approximately 620 MA/cm² at 4.2 K in a width of 30 nm bridges, and increased by about two orders of magnitude in the different widths of J_c. The critical temperature T_c was 87 K, about the same as T_c of the film. The current-voltage characteristics showed a different curve from the conventional flux-flow type as the widths have been narrowed. Nanobridges developed in this study are expected to the applications for nano-SQUIDs or the optical input/output interfaces in single-flux-quantum circuits.