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Right scale: Resistance as a function of temperature for the two proximity SQUIDs shown in the inset, the data are taken using an ac measurement current of . Left scale: Temperature dependence of the critical current derived from differential resistance vs bias current measurements for the upper one of the two devices. The ac measurement currents are above and below . Below , the retrapping currents (open circles) are clearly different from the switching currents (solid circles), indicating hysteresis. Inset: Schematic of the four-probe measurement configuration and SEM images of the two devices. The arms of the loops (brighter wires) are made of Au, and the electrodes extending out of the top and bottom (darker wires) are made of Al. The size bar in both images is .
Magnetoresistance of the top loop in Fig. 1 at for different dc bias currents. The applied flux is measured in units of superconducting flux quanta, , corresponding to a field of for this device. With increasing bias current, the oscillation evolves from periodic oscillations to periodic oscillations and then to inverted oscillations.
(a) dc bias current dependence of the differential resistance at for different applied magnetic fluxes. The three vertical arrows indicate where two curves cross each other. (b) From the bottom up, the differential magnetoresistances at , , and , respectively, showing the evolution to oscillations. The two upper curves are offset by 15 and , respectively, for clarity.
Differential magnetoresistances at 0.3 and with dc bias current set close to the differential resistance peak. The periodic peaks in the magnetoresistance are mostly absent at , likely due to the peak width at this temperature being smaller than the measurement current.
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