Coexistence and tuning of spin-singlet and triplet transport in spin-filter Josephson junctions

Heterostructures comprising of different materials provide the possibility to engineer devices with specific properties based on the individual characteristics and interactions between the different components. Here, the authors report the detection of proximity-induced spin-triplet Cooper pairs in a superconductor/ferromagnet/superconductor Josephson junction made of NbN and GdN respectively. The increased capabilities of coupling more and more materials through functional interfaces are paving the way to a series of exciting experiments and extremely advanced devices. Here we focus on the capability of magnetically inhomogeneous superconductor/ferromagnet (S/F) interfaces to generate spin-polarized triplet pairs. We build on previous achievements on spin-filter ferromagnetic Josephson junctions (JJs) and find direct correspondence between neat experimental benchmarks in the temperature behavior of the critical current and theoretical modelling based on microscopic calculations, which allow to determine a posteriori spin-singlet and triplet correlation functions. This kind of combined analysis provides an accurate proof of the coexistence and tunability of singlet and triplet transport. This turns to be a powerful way to model disorder and spin-mixing effects in a JJ to enlarge the space of parameters, which regulate the phenomenology of the Josephson effect and could be applied to a variety of hybrid JJs.