MoRe/YBCO Josephson junctions and pi-loops

We have developed Josephson junctions between the d-wave superconductor YBa2Cu3O7-x (YBCO) and the s-wave Mo0.6Re0.4 (MoRe) alloy superconductor (ds-JJs). Such ds Josephson junctions are of interest for superconducting electronics making use of incorporated pi-phase shifts. The I(V)-characteristics of the ds-JJs demonstrate a twice larger critical current along the [100] axis of the YBCO film compared to similarly-oriented ds-JJs made with a Nb top electrode. The characteristic voltage IcRn of the YBCO-Au-MoRe ds-JJs is 750 mu V at 4.2 K. The ds-JJs that are oriented along the [100] or [010] axes of the YBCO film exhibit a 200 times higher critical current than similar ds-JJs oriented along the [110] axis of the same YBCO film. A critical current density J(c) = 20 kA cm(-2) at 4.2 K was achieved. Different layouts of pi-loops based on the novel ds-JJs were arranged in various mutual coupling configurations. Spontaneous persistent currents in the pi-loops were investigated using scanning SQUID microscopy. Magnetic states of the pi-loops were manipulated by currents in integrated bias lines. Higher flux states up to +/- 2.5 Phi(0) were induced and stabilized in the pi-loops. Crossover temperatures between thermally activated and quantum tunneling switching processes in the ds-JJs were estimated. The demonstrated ability to stabilise and manipulate states of pi-loops paves the way towards new computing concepts such as quantum annealing computing.