Abstract
Step-edge junctions represent one type of grain boundary Josephson junctionemployed in high-temperature superconducting junction technology. To date, themajority of results published in the literature focus on [001]-tilt grain boundaryjunctions (GBJs) produced using bicrystal substrates. We investigate the stepmorphology and YBCO (yttrium barium copper oxide) film structure of YBCO-basedstep-edge junctions on MgO [001] substrates which structurally resemble [100]-tiltjunctions. High-resolution electron microscopy reveals a clean GBJ interface of width ∼ 1 nm and a single junction at the top edge. The dependence of the transport propertieson the MgO step-edge and junction morphology is examined at 4.2 K, to enabledirect comparison with results for other junction studies such as [001]-tiltand [100]-tilt junctions and building on previously published 77 K data. MgOstep-edge junctions show a slower reduction in critical current density withstep angle compared with [001]-tilt junctions. For optimized step parameters,transport measurements revealed large critical current and normal resistance (IcRN) products(∼3–5 mV), comparable with the best results obtained in other kinds of [100]-tilt GBJs inYBCO at 4.2 K. Junction-based devices such as SQUIDs (superconducting quantuminterference devices) and THz imagers show excellent performance when MgO-basedstep-edge junctions are used.
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