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

A controllable p-SQUID is a DC SQUID ~direct-current superconducting quantum interference device! with two controllable p junctions as weak links. A controllable p 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 Vc over these contacts it is possible to control the state of the junction, i.e., a conventional ~0! state or a p state, depending on the magnitude of Vc . We demonstrate experimentally that, by putting one junction into a p state, a screening current is generated around the SQUID loop at an integer external flux. To be able to do this, we have fabricated controllable p junctions, based on Cu-Nb or Ag-Nb, in a new geometry. We show that at 1.4 K only the Ag-Nb device shows the transition to a p state as a function of Vc consistent with theoretical predictions. In a controllable p-SQUID based on Nb-Ag we observe, apart from a screening current at integer external flux, a phase shift of p of the VSQUID2B oscillations under a suitable current bias, depending on the magnitude of Vc .