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The continuous development of superconducting electronics is encouraging several studies on hybrid Josephson junctions (JJs) based on superconductor-ferromagnet-superconductor (SFS) heterostructures, as either spintronic devices or switchable elements in quantum and classical circuits. Recent experimental evidence of macroscopic quantum tunneling and of an incomplete 0-$\ensuremath{\pi}$ transition in tunnel-ferromagnetic spin-filter JJs could also enhance the capabilities of SFS JJs as active elements. Here, we provide a self-consistent electrodynamic characterization of $\mathrm{Nb}\mathrm{N}$/$\mathrm{Gd}\mathrm{N}$/$\mathrm{Nb}\mathrm{N}$ spin-filter JJs as a function of the barrier thickness, disentangling the high-frequency dissipation effects due to the environment from the intrinsic low-frequency dissipation processes. The fitting of the $I$-$V$ characteristics at 4.2 K and at 300 mK by using the tunnel-junction-microscopic model allows us to determine the subgap resistance ${R}_{\mathrm{sg}}$, the quality factor $Q$, and the junction capacitance $C$. These results provide the scaling behavior of the electrodynamic parameters as a function of the barrier thickness, which represents a fundamental step for the feasibility of tunnel-ferromagnetic JJs as active elements in quantum and classical circuits, and are of general interest for tunnel junctions other than conventional SIS JJs.

Triplet supercurrents in multilayer ferromagnetic Josephson junctions with misaligned magnetization can penetrate thicker ferromagnetic barriers compared to the singlet component. Although the static properties of these junctions have been extensively studied, the dynamic characteristics remain largely unexplored. Here we report a comprehensive electrodynamic characterization of multilayer ferromagnetic Josephson junctions composed of Co and Ho. By measuring the temperature-dependent current-voltage characteristics and the switching current distributions down to 0.3 K, we show that phase dynamics of junctions with triplet supercurrents exhibits long (in terms of proximity) junction behavior and moderately damped dynamics with renormalized capacitance and resistance. This unconventional behavior possibly provides a different way to dynamically detect triplets. Our results show new theoretical models are required to fully understand the phase dynamics of triplet Josephson junctions for applications in superconducting spintronics., DM, RC, FT would like to thank NANOCOHYBRI project (Cost Action CA 16218). NB acknowledges funding from the British Council through UKIERI programme and Loughborough University. MGB acknowledges funding from EPSRC Programme Grant EP/N017242/1.

The interfacial coupling of two materials with different ordered phases, such as a superconductor (S) and a ferromagnet (F) is driving new fundamental physics and innovative applications. For example, the creation of spin-filter Josephson junctions and the demonstration of triplet supercurrents have suggested the potential of a dissipationless version of spintronics based on unconventional superconductivity. Here we demonstrate evidence for active quantum applications of S-F-S junctions, through the observation of macroscopic quantum tunneling in Josephson junctions with GdN ferromagnetic insulator barriers. We prove a clear transition from thermal to quantum regime at a crossover temperature of about 100 mK at zero magnetic field in junctions which demonstrate a clear signature of unconventional superconductivity. Following previous demonstration of passive S-F-S phase shifters in a phase qubit, our result paves the way to the active use of spin filter Josephson systems in quantum hybrid circuits., Comment: 16 pages, 4 figures

A ferromagnetic Josephson junction (JJ) represents a special class of hybrid system where different ordered phases meet and generate novel physics. In this work we report on the transport measurements of underdamped ferromagnetic NbN/GdN/NbN JJs at low temperatures. In these junctions the ferromagnetic insulator gadolinium nitride barrier generates spin-filtering properties and a dominant second harmonic component in the current-phase relation. These features make spin filter junctions quite interesting also in terms of fundamental studies on phase dynamics and dissipation. We discuss the fingerprints of spin filter JJs, through complementary transport measurements, and their implications on the phase dynamics, through standard measurements of switching current distributions. NbN/GdN/NbN JJs, where spin filter properties can be controllably tuned along with the critical current density (J c ), turn to be a very relevant term of reference to understand phase dynamics and dissipation in an enlarged class of JJs, not necessarily falling in the standard tunnel limit characterized by low J c values.

We report on $\hbox{YBa}_{2}\hbox{Cu}_{3}\hbox{O}_{7-x} $ biepitaxial grain boundary Josephson junctions (JJs) demonstrating significant tunability of their circuital parameters. We show how the enhanced control of the junction properties, and particularly of the capacitance, leads to advances in the understanding of phase dynamics of high-critical-temperature superconductor JJs and potentially of their intrinsic dissipation mechanisms.

We have identified anomalous behavior of the escape rate out of the zero-voltage state in Josephson junctions with a high critical current density Jc. For this study we have employed YBa2Cu3O7-x grain boundary junctions, which span a wide range of Jc and have appropriate electrodynamical parameters. Such high Jc junctions, when hysteretic, do not switch from the superconducting to the normal state following the expected stochastic Josephson distribution, despite having standard Josephson properties such as a Fraunhofer magnetic field pattern. The switching current distributions (SCDs) are consistent with nonequilibrium dynamics taking place on a local rather than a global scale. This means that macroscopic quantum phenomena seem to be practically unattainable for high Jc junctions. We argue that SCDs are an accurate means to measure nonequilibrium effects. This transition from global to local dynamics is of relevance for all kinds of weak links, including the emergent family of nanohybrid Josephson junctions. Therefore caution should be applied in the use of such junctions in, for instance, the search for Majorana fermions., Comment: 8 pages, 4 figures