Direct demonstration of circulating currents in a controllable $π$-SQUID generated by a 0 to $π$ transition of the weak links

Details Direct demonstration of circulating currents in a controllable $π$-SQUID generated by a 0 to $π$ transition of the weak links Direct demonstration of circulating currents in a controllable $π$-SQUID generated by a 0 to $π$ transition of the weak links

2002-03-21

arxiv.org/abs/cond-mat/0203433v1

Physics

Condensed Matter

Superconductivity

11 pages, 12 figures, subm. to Phys. Rev. B

Scientific paper

10.1103/PhysRevB.65.224513

A controllable $\pi$-SQUID is a DC SQUID with two controllable $\pi$-junctions as weak links. A controllable $\pi$-junction consists of a superconducting - normal metal - superconducting Josephson junction with two additional contacts to the normal region of the junction. By applying a voltage $V_c$ over these contacts it is possible to control the sate of the junction, i.e. a conventional (0) state or a $\pi$-state, depending on the magnitude of $V_c$. We demonstrate experimentally that, by putting one junction into a $\pi$-state, a screening current is generated around the SQUID loop at integer external flux. To be able to do this, we have fabricated controllable $\pi$-junctions, based on Cu-Nb or Ag-Nb, in a new geometry. We show that at 1.4 K only the Nb-Ag device shows the transition to a $\pi$-state as a function of $V_c$ consistent with theoretical predictions. In a controllable $\pi$ SQUID based on Nb-Ag we observe, a part from a screening current at integer external flux, a phase shift of $\pi$ of the $V_{SQUID}-B$ oscillations under suitable current bias, depending on the magnitude of $V_c$.

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