Two-dimensional magnetic field dependence of zero and finite voltage steps in current–voltage characteristics of superconducting quantum interference devices

• SQUID with two Nb/Al-oxide/Nb junctions fabricated.
• Josephson current Ic dependence on Hx, Hy external magnetic field was obtained.
• Finite voltage steps Istep on Hx, Hy external magnetic field was also measured.
• Resonant electromagnetic field explained the finite voltage steps.

Modulation characteristics of Josephson current through superconducting quantum interference devices (SQUIDs) by two dimensional scanning of external magnetic field have been studied. Vertical type SQUIDs composed of two niobium/aluminum-oxide/niobium (Nb/Al-oxide/Nb) tunnel junctions are fabricated using magnetron sputtering system. In order to measure the magnetic dependence of the critical current Ic through SQUIDs, Hx and Hy magnetic field components parallel to junction edges are scanned in two dimensions (2-D) by using two pairs of Helmholtz coils driven in GPIB (General Purpose Interface Bus) system. The 2-D magnetic field (Hx, Hy) dependences of the Josephson current Ic and the resonant current steps Istep at finite voltage in the current–voltage curves of SQUIDs have been obtained. Modulation characteristics of SQUIDs with different junction separation are measured. The resonant current steps Istep are also studied using superconducting planar circuit model.

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