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

J. J. A. Baselmans; B. J. van Wees; T. M. Klapwijk

doi:10.1103/PhysRevB.65.224513

paper

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

arXiv:cond-mat/0203433 · doi:10.1103/PhysRevB.65.224513

Abstract

A controllable $π$ -SQUID is a DC SQUID with two controllable $π$ -junctions as weak links. A controllable $π$ -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 $π$ -state, depending on the magnitude of $V_{c}$ . We demonstrate experimentally that, by putting one junction into a $π$ -state, a screening current is generated around the SQUID loop at integer external flux. To be able to do this, we have fabricated controllable $π$ -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 $π$ -state as a function of $V_{c}$ consistent with theoretical predictions. In a controllable $π$ SQUID based on Nb-Ag we observe, a part from a screening current at integer external flux, a phase shift of $π$ of the $V_{S Q U I D} - B$ oscillations under suitable current bias, depending on the magnitude of $V_{c}$ .

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

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The controllable pi - SQUID

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

Abstract

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