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(Color online) Schematic views of annular Josephson junction stacks. (a) A half-finished sample (one side already structured), (b) a finished sample (another side also structured), and (c) the optical microscopic photo of a sample with four (BSCCO) annular stacks integrated on one chip. Every stack can be measured individually with four of the ten superconducting electrodes.
Current-voltage characteristics of a BSCCO annular stack with a mean circumference of (Ring-144) without or with Josephson fluxons trapped. The dashed guidelines marked with A–E show the bias sequence. From B to C, Josephson fluxons can be trapped, and the trapped state can be adjusted by sweeping current forward and backward along C. The thick zero-voltage line indicates Josephson junctions free of fluxons before switching to finite voltage. The thick finite-voltage line, the McCumber state of all junctions, has no visible change before and after trapping. The thinner lines and the inset show the multiple branches after trapping.
Microwave responses of an annular stack with a mean circumference of under microwave irradiation at 13.6 or .
(a) characteristics of Ring-97 (with a mean circumference of ) with fluxons trapped, and (b) the microwave response at . (c) characteristics of Ring-144 (with a mean circumference of ) with fluxons trapped, and (d) the microwave response at . Noticeably, in the experiments, only junctions trapped with fluxons give rise to Shapiro steps under microwave irradiation.
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