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
YBa
₂
Cu
₃
O
_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/cm
²
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.