YBa2Cu307./j-Based, Edge-Geometry SNS Josephson Junctions with Low-resistivity PrBa2Cu307-~ Barriers

We investigated the properties of all-high-Tc edge-geometry Josephson weak links using superconducting YBa2Cu307+ (YBCO) electrodes and PrBa2Cu307-~ (PBCO) normal-metal layers. The fabrication of the weak-links involved first ionmilling the base YBCO film using a MgO mask to form the edge and then depositing PBCO and YBCO layers in situ by pulsed-laser deposition. The optimum PBCO films had resistivities of 2 to 4 mQ cm at room temperature and -30 mQ cm at 4.2 K. Current-versus-voltage (I-V) characteristics were qualitatively consistent with the resistively-shunted-junction (RN) model. Strong Shapiro steps were present in the I-V characteristics of junctions under microwave irradiation and the critical current of the devices modulated with a Fraunhofer-like dependence as a function of magnetic field. The device parameters exhibited good scaling with area and PBCO thickness. The critical-current density varied exponentially with PBCO thickness, yielding a normal-metal coherence length of 9 nm for the PBCO.