Transport properties of YBCO step edge Josephson junction with different step angles.

Step edge Josephson junctions are fabricated with varying step angles ranging from 10° to 35° on the MgO (100) single-crystal substrate. The impact of step angle on the transport characteristics of the step edge junction is studied. It is found that as the step angle increases, the critical current (Ic) of the junction drops while its normal state resistance (Rn) rises. The overall IcRn product is found to be increasing with an increase in the step angle at all temperatures from 68 K to 77 K. For the 35° step angle junction, the IcRn value is obtained to be 0.34 mV at 77 K, which is comparable to the best values of IcRn products at 77 K so far. For lower step angle junctions, the superconductor grain to grain coupling exhibits more superconductor-normal-superconductor (SNS) type behavior, but as the step angle increases, the superconductor-insulator-superconductor (SIS) type behavior becomes apparent. MgO-based step edge junctions perform well in SQUID and terahertz detection applications. [ABSTRACT FROM AUTHOR]