Abstract
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 π-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 μV 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 Jc = 20 kA cm−2 at 4.2 K was achieved. Different layouts of π-loops based on the novel ds-JJs were arranged in various mutual coupling configurations. Spontaneous persistent currents in the π-loops were investigated using scanning SQUID microscopy. Magnetic states of the π-loops were manipulated by currents in integrated bias lines. Higher flux states up to ±2.5Φ0 were induced and stabilized in the π-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 π-loops paves the way towards new computing concepts such as quantum annealing computing.
Highlights
Many superconducting devices, such as SQUIDs, flux qubits, RSFQ circuits, etc, require biasing by magnetic flux for their optimal operation
The ds-Josephson junction (JJ) 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
Magnetic states of the π-loops were manipulated by currents in integrated bias lines
Summary
Many superconducting devices, such as SQUIDs, flux qubits, RSFQ circuits, etc, require biasing by magnetic flux for their optimal operation. Miniaturization of such superconducting circuits becomes difficult because ever higher magnetic fields. Integration of phase shifters can avoid the need for external current sources to generate high bias magnetic fields in nanoscale devices [1]. We describe ramp-type YBCO–Au– MoRe (YBCO–MoRe) ds-JJs on graphoepitaxially buffered MgO substrates This is the first time that the MoRe alloy is used as an s-wave superconductor in ds-JJs. This is the first time that the MoRe alloy is used as an s-wave superconductor in ds-JJs For these ds-JJs, we investigated microstructural properties and measured I(V)characteristics in different directions. Higher magnetic states of the π-loops beyond the ±0.5Φ0 ground states were induced by currents in integrated bias lines and stabilized at zero field
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