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Atomic force micrographs of 8 nm thick, 30 nm wide aluminum nanobridges contacted with (a) 8 nm thick 2D banks and (b) 80 nm thick 3D banks. Two nanobridge junctions are incorporated into an unshunted dc SQUID, as shown in (b). The SQUID loop is , and is calculated to have 5 pH of inductance.
product as a function of bridge length for both 2D and 3D nanoSQUIDs from several chips. The dashed line in the main figure is the zero temperature prediction for a short metallic weak link connected to ideal phase reservoirs. Inset: a typical I-V curve for a 3D nanoSQUID, consisting of two 75 nm bridges.
Critical current as a function of applied magnetic flux for 75, 150, and 250 nm long nanoSQUIDs. The upper panel shows experimental results for nanobridges with 3D banks and the lower panel for 2D banks.
Critical current modulation depth as a function of device length for both 3D and 2D nanobridges. The thick dashed line at the top is the theoretical prediction for an ideal weak link SQUID at zero temperature with zero loop inductance. The thinner dashed lines are numerical calculations for our 3D (middle line) and 2D (lower line) devices, including the effect of finite loop inductance.
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