Magnetic field behavior of small sputtered step-edge junctions

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Abstract
YBa2Cu3O7 step‐edge junctions with widths down to 0.5 μm are fabricated on SrTiO3 substrates by Ar ion‐beam milling of the steps, high‐pressure on‐axis magnetron sputtering, electron beam patterning and ion‐beam etching of the microbridge. For ratios of film thickness to step height of ∼1/2 the current‐voltage characteristics show Shapiro steps under microwave irradiation and resistively shunted junction like behavior. The periodic dependence of the critical current upon the magnetic field resembles a Fraunhofer pattern. The period of the current variation ΔB0 depends upon the width w of the junction according to the theoretical prediction for planar thin Josephson junctions: ΔB0=1.84φ0/w2. Junctions with widths of 0.7 μm possess a large magnetic field stability with ΔB0≊100 G. Small junctions (w<1 μm) exhibit voltage jumps in the Fraunhofer pattern, which are explained by flux penetration of single vortices into the electrodes.

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