Superconducting properties of YBa₂Cu₃O₇step-edge Josephson junctions prepared on CeO₂-buffered sapphire substrates

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Step-edge Josephson junctions in the c -axis oriented YBa 2 Cu 3 O 7 films were fabricated on the CeO 2 -buffered sapphire substrates. The step angles were controlled in the wide range of 20-75° by an Ar ion milling technique. The I - V curves of junctions fabricated on the 35° step with the film thickness to the step height ratio of about 0.8 exhibited a resistively shunted junction-like behaviour with an I C R N product of about 250 µV and a critical current density of about 2 × 10 4 A cm -2 at 77 K. The critical currents of the step-edge junctions increased approximately linearly with decreasing temperature but the normal resistance remained almost constant. All the samples of the step-edge Josephson junctions satisfied a scaling behaviour of I C R N ∝( J C ) 0.5 , and a dc SQUID made out of those junctions exhibited a typical voltage modulation in an applied magnetic field.