Properties of YBaCuO nanobridges and dc-SQUIDs

Abstract

YBaCuO nanobridges and inductively shunted dc-SQUIDS have been patterned by direct Focused Ion Beam milling. ~anobridges manifest true Josephson effect, which can be expla~ned by coherent motion of Abrikosov vortices in the bridge. An enhancement of this effect is proposed to be due to local suppression of the superconducting properties within the nanobridge area. This leads to a transition from SNS to SS'S type b e h a v i~~ of the nano ridge with decreasing temperature. TempErature d e~e n d~n c e of the critical current, dynamic resistance, and SQUID voltage-flux modulation is discussed. The flux noise level of the nanoSQUID is measured to be about 6.5 p@&€z at 62.7 K.

Why NanoSQUIDs are important: an introduction to the focus issue

“…At 78 K, Josephson-like behaviour was observed with strong fluxflow behaviour at temperatures under 76 K. The voltage-flux characteristic curves, V -I mod , of the nanoSQUID at different bias currents at 78 K were observed. The measurements suggested that the weak-link structure was a superconducting metal with a critical temperature smaller than that of washer YBa 2 Cu 3 O 7−x , as also conjectured in [2,3].…”

“…Applications were limited by the kinetic inductance and the mechanical and electrical fragility of the devices. The University of Twente group [2,3] went on to fabricate nanobridges in dc SQUIDs in YBCO using focused ion beams. They achieved a fluxlocked loop measurement with an effective input flux noise of 6.5 μϕ 0 Hz −1/2 at 62.7 K. Shrinking down the SQUID washer dimensions, in addition to the junction dimensions, was initially suggested by Ketchen et al [4] who determined the specification of a SQUID that could measure single atomic spins; a holy grail for physical measurement.…”

Ratchet Effect of Single Vortex Motion in Superconducting Asymmetrical Nanobridges

“…Nanobridges are also known to work as a vortex gate, in which the motion of a single Abrikosov vortex is controlled. 2,3) The physical behavior of a vortex in a nanobridge plays a significant role in its current-voltage (I-V ) characteristics. The critical current, I c , of a nanobridge is determined by the surface barrier to vortex entry.…”

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

“…To establish such techniques affects those of future HTS-SFQ circuits [4]. The dc-SQUIDs consisting of nanobridges have been demonstrated and reported so far [1], [6]. However, nanobridges in less than 100 nm range have poor reproducibility.…”