Abstract
The interplay between superconducting and ferromagnetic order pa¬rameters in S/F interfaces gives rise to a wide range of peculiar properties with applications in high-efficiency computation and in the emerging field of super¬conducting spintronics. In NbN/GdN/NbN Josephson junctions, GdN barriers give unique properties due to the double insulting and ferromagnetic nature of the material, as demonstrated in previous works. Here we focus on tunneling spectroscopy of these junctions down to 0.3 K when changing the barrier thick¬ness, which contributes to complete a consistent picture on the physics of these junctions and supports the previous indications of equal-spin Cooper pairs con¬tributing to the total supercurrent of the devices.
Highlights
In the last twenty years, the advancements in thin film deposition have made possible the realization of superconductor/ferromagnet heterostructures, and a subsequent rich literature on the experimental characterization and the theoretical modeling of such systems
Spin filter Josephson junctions are characterized by a barrier with the unique double nature of ferromagnet and insulator
In junctions with high spin polarization, Eq 2 describing the quasi-particle current gives a very rough reproduction of the measured dI/dV curve. This result can be compared with the one reported in [7], where the IC(T ) behavior can be only roughly reproduced without considering a much more complex magnetic structure of the barrier, including a strong asymmetry in the induced exchange fields. These experimental indications of an increasing asymmetry in the exchange fields induced in the NbN electrodes coming from both dI/dV measurements and IC(T ) curves [Fig. 2 (c), (g) and (k)] are compatible with the presence of spin-triplet transport mechanisms contributing to the total supercurrent in spin-filter Josephson junctions
Summary
In the last twenty years, the advancements in thin film deposition have made possible the realization of superconductor/ferromagnet heterostructures, and a subsequent rich literature on the experimental characterization and the theoretical modeling of such systems. Most of this literature focuses on metallic junctions, employing a wide range of ferromagnets as weak links. Spin filter Josephson junctions are characterized by a barrier with the unique double nature of ferromagnet and insulator. We present conductance measurements confirming the previous indications of equal-spin coupling inside the barrier
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