Observation of 0–π transition in SIsFS Josephson junctions

Abstract

The 0–π transition in Superconductor-Insulator-superconductor-Ferromagnet-Superconductor (SIsFS) Josephson junctions (JJs) was investigated experimentally. As predicted by theory, an s-layer inserted into a ferromagnetic SIFS junction can enhance the critical current density up to the value of an SIS tunnel junction. We fabricated Nb′ | AlOx | Nb | Ni60Cu40 | Nb JJs with wedge-like s (Nb) and F (Ni60Cu40) layers and studied the Josephson effect as a function of the s- and F-layer thickness, ds and dF, respectively. For ds = 11 nm, π-JJs with SIFS-type jc(dF) and critical current densities up to jcπ=60 A/cm2 were obtained at 4.2 K. Thicker ds led to a drastic increase of the critical current decay length, accompanied by the unexpected disappearance of the 0–π transition dip in the jc(dF) dependence. Our results are relevant for superconducting memories, rapid single flux quantum logic circuits, and solid state qubits.

The effect of normal and insulating layers on 0-πtransitions in Josephson junctions with a ferromagnetic barrier

“…This conclusion is also supported by experimental observations on SIsFS junctions [54][55][56]. These observations indicate that the introduction of a thin s interlayer, which should make a transition to the normal state if its thickness is of the order of the coherence length, shifts the 0-π transitions towards larger d .…”

Ferromagnetic Josephson junctions based on epitaxial NbN/Ni60Cu40/NbN trilayer

“…The weakly ferromagnet NiCu was often used in fabrication of Nb based ferromagnetic Josephson junction. [21][22][23] The thickness of each layer was controlled by measuring the deposition rate and the deposition time. The deposition rate of the NbN and Ni 60 Cu 40 layers was 0.6 nm/s and 0.07 nm/s, respectively.…”

Current-phase relations in SIsFS junctions in the vicinity of 0- π transition

“…Recent theoretical 5 and experimental 6 studies indicated a possible realization of the above mentioned transformations of I S (ϕ) in SIsFS structures in the form of instabilities near 0-π transition. So far, this new fundamental feature of the Josephson structures remains unexplored.…”