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(Color) Schematic of (a) a phase-shifting element consisting of four Josephson junctions and a built-in phase shift, and (b) a switchable SQUID, in which a SQUID loop incorporates the phase shifter (dashed rectangle) and an unbiased four-junction loop. (c). Implementation of the switchable SQUID. From substrate to top layer the structure consists of a tetra layer of , a Au barrier (not visible), and Nb counterelectrode (blue). All junctions are oriented along the ⟨100⟩-crystal directions of the high- material (white arrows), facing the maximum gap of the order parameter.
Critical current versus applied magnetic field for a reference SQUID incorporating two unbiased four-junction loops (top), and for the two complementary states of the switchable SQUID (middle and bottom).
Current versus voltage characteristics at various magnetic fields for (a)–(c) the switchable SQUID, and (d) the reference SQUID. The characteristics (a) and (b) are recorded for small amplitudes of the bias current sweep, stably showing both complementary states of the SQUID, whereas the characteristics (c) and (d) are recorded for large values of the bias current sweep. (c) displays the bistable character of the SQUID, when the bias current amplitude exceeds the threshold value of about .
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