MoRe/YBCO Josephson junctions and π-loops

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 I c R n 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 J c = 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.

Superconducting Proximity Effect in d‐Wave Cuprate/Graphene Heterostructures

“…[7] Furthermore, the combination of high-T C and the 𝜋 phase shift between d-wave lobes can be used for designing topological Josephson junction hosting Majorana bound states. [78][79][80] Although extended to different d-wave/s-wave Josephson junctions, [81] so far these 𝜋 junctions have not been explored using Dirac materials (and particularly graphene) as Josephson barrier. Yet, these devices would be endowed with an interesting property, namely tunability, by replacing the usual passive weak link by a gate-tunable Dirac material.…”

Planar MoRe-based direct current nanoSQUID

“…MoRe is a type-II superconductor for which the magnetic and transport properties have been studied since the 1960's [38][39][40][41]. The employment of Mo 0.6 Re 0.4 alloy for s-wave superconductors in JJs was demonstrated recently [42]. MoRe thin films are relatively easily achieved by magnetron sputtering, slightly susceptible to oxidation at ambient conditions, and suitable for electron beam lithography.…”

Quantum size effects in ultra-thin YBa2Cu3O7-x films

“…The nodal critical current density of the thickest nanowire is signi cantly smaller than those in the antinodal directions, as expected in the case of the d x2−y2 -wave pairing symmetry. However, the < J c45 >/<J c0 > and < J c45 >/<J c90 > ratios are not as small as in bulk samples, where they are about a few percent 18,19 . Remarkably, the < J c45 > thickness dependence is different from those in the antinodal directions.…”