Abstract:We fabricated and characterized a weakly coupled magnetic Josephson junction based on epitaxial NbN/Ni60Cu40/NbN trilayer heterostructures on single crystal MgO (100) substrates. X-ray diffraction and cross-sectional scanning transmission electron microscopy were used to verify the epitaxial growth of NbN/Ni60Cu40/NbN trilayer, while the ferromagnetic properties of NiCu on NbN film were recorded by plotting the magnetization as a function of both the temperature and the magnetic field strength. The NbN/Ni60Cu4… Show more
“…This value is higher than that extracted from the resistivity of a single Pd 89 Ni 11 film (~ 90 µΩ) 31 , which may be due to the interface resistance arising in the non-epitaxial NbN counter-layer grown on PdNi. However, this interface resistance is much smaller than that reported for NbN/CuNi/NbN junctions 32 , in which the interface resistance was seven-fold larger than the resistance extracted from the resistivity of a single CuNi film. Figure 3 ( a ) Current–voltage characteristics of a 10 × 10 µm 2 junction with a 25-nm-thick PdNi interlayer measured at 4.2 K. ( b ) Dependence of critical currents on the thickness of the PdNi interlayer.…”
We studied niobium nitride (NbN)-based π-junctions with a diluted ferromagnetic Pd89Ni11 interlayer (NbN/PdNi/NbN junctions). In the NbN/PdNi/NbN junctions with various PdNi thicknesses, we observed a non-monotonic dependence of the critical currents on PdNi thickness, indicating the effects of the exchange interaction on the superconducting order parameter. From theoretical fitting of the experimental data, we found that the NbN/PdNi/NbN junctions showed a significantly smaller degree of spin-flip scattering in the PdNi interlayer than in the CuNi interlayer of NbN/CuNi/NbN junctions reported previously. The weak spin-flip scattering leads to a longer decay length of the Josephson critical current, so the critical currents were observed over a wide range of PdNi thicknesses (10–40 nm). We also fabricated superconducting quantum interference devices (SQUIDs) including the NbN/PdNi/NbN junction, using a PdNi thickness in which the π-state was expected. A half-flux-quantum shift, as evidence of the π-state, was observed in the magnetic field-dependent critical currents of the SQUIDs. This result represents an important step towards the practical application of NbN-based π-Josephson junctions.
“…This value is higher than that extracted from the resistivity of a single Pd 89 Ni 11 film (~ 90 µΩ) 31 , which may be due to the interface resistance arising in the non-epitaxial NbN counter-layer grown on PdNi. However, this interface resistance is much smaller than that reported for NbN/CuNi/NbN junctions 32 , in which the interface resistance was seven-fold larger than the resistance extracted from the resistivity of a single CuNi film. Figure 3 ( a ) Current–voltage characteristics of a 10 × 10 µm 2 junction with a 25-nm-thick PdNi interlayer measured at 4.2 K. ( b ) Dependence of critical currents on the thickness of the PdNi interlayer.…”
We studied niobium nitride (NbN)-based π-junctions with a diluted ferromagnetic Pd89Ni11 interlayer (NbN/PdNi/NbN junctions). In the NbN/PdNi/NbN junctions with various PdNi thicknesses, we observed a non-monotonic dependence of the critical currents on PdNi thickness, indicating the effects of the exchange interaction on the superconducting order parameter. From theoretical fitting of the experimental data, we found that the NbN/PdNi/NbN junctions showed a significantly smaller degree of spin-flip scattering in the PdNi interlayer than in the CuNi interlayer of NbN/CuNi/NbN junctions reported previously. The weak spin-flip scattering leads to a longer decay length of the Josephson critical current, so the critical currents were observed over a wide range of PdNi thicknesses (10–40 nm). We also fabricated superconducting quantum interference devices (SQUIDs) including the NbN/PdNi/NbN junction, using a PdNi thickness in which the π-state was expected. A half-flux-quantum shift, as evidence of the π-state, was observed in the magnetic field-dependent critical currents of the SQUIDs. This result represents an important step towards the practical application of NbN-based π-Josephson junctions.
“…However, this interface resistance is much smaller than that reported for NbN/CuNi/NbN junctions 32 , in which the interface resistance was seven-fold larger than the resistance extracted from the resistivity of a single CuNi film.…”
We studied niobium nitride (NbN)-based π-junctions with a diluted ferromagnetic Pd89Ni11 interlayer (NbN/PdNi/NbN junctions). In the NbN/PdNi/NbN junctions with various PdNi thicknesses, we observed a non-monotonic dependence of the critical currents on PdNi thickness, indicating the effects of the exchange interaction on the superconducting order parameter. From theoretical fitting of the experimental data, we found that the NbN/PdNi/NbN junctions showed a significantly smaller degree of spin-flip scattering in the PdNi interlayer than in the CuNi interlayer of NbN/CuNi/NbN junctions reported previously. The weak spin-flip scattering leads to a longer decay length of the Josephson critical current, so the critical currents were observed over a wide range of PdNi thicknesses (10 – 40 nm). We also fabricated superconducting quantum interference devices (SQUIDs) including the NbN/PdNi/NbN junction, using a PdNi thickness in which the π-state was expected. A half-flux-quantum shift, as evidence of the π-state, was observed in the magnetic field-dependent critical currents of the SQUIDs. This result represents an important step towards the practical application of NbN-based π-Josephson junctions.
“…[9] All of the SFS Josephson junctions reported here were fabricated in our laboratory using a process as described elsewhere. [20] The chemical stoichiometry of the The exchange energy exerted on the Cooper pair could induce a non-zero momentum center, resulting in the damped oscillation behavior of the critical current as a function of the ferromagnetic layer thickness.…”
We fabricate high quality superconductor/ferromagnet/superconductor (SFS) Josephson junctions using epitaxial NbN/Ni60Cu40/NbN trilayer heterostructures. Both experimental measurements and theoretical calculations of the ferromagnet layer thickness dependence of the Josephson critical current are performed. We observe the damped oscillation behavior of the critical current as a function of the ferromagnetic layer thickness at 4.2 K, which shows a 0-𝜋 phase transition in this type of magnetic Josephson junction. Clear 0-𝜋 and reverse 𝜋-0 phase transitions occur around the Ni60Cu40 thicknesses of 3.2 and 6.7 nm. Numerical calculations based on the quasi-classical Usadel equation and the Green function fit well with the experimental results. Compared with the dirty limit, the intermediate regime without the dead layer gives better fit for our SFS Josephson junctions because of the epitaxial structure. Both of the 0-and 𝜋-phase junctions show the ideal magnetic field dependence with a Fraunhofer-like pattern at 4.2 K.
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