A new study published in *Physical Review Letters*, from a collaboration between the Centro de Física de Materiales (San Sebastián), the Instituto de Ciencia de Materiales de Madrid (both CSIC), and the IFIMAC – Condensed Matter Physics Center at the Universidad Autónoma de Madrid, reports the first experimental observation of subgap transport in Josephson junctions based on spin-split superconductors. The devices combine aluminum (Al) with the ferromagnetic insulator europium sulfide (EuS) — a platform pioneered in San Sebastián, the first European lab to achieve spin splitting without an external magnetic field in this type of superconductor. The key finding is a striking even-odd effect in Multiple Andreev Reflections (MAR): odd-order processes are split by the magnetic exchange interaction of EuS, while even-order ones remain unaffected — an unambiguous signature of coexisting superconductivity and magnetism. The study further shows that a sizeable Josephson current survives in the presence of magnetic interactions, confirming that Cooper pairs maintain quantum coherence under these conditions. Beyond fundamental interest, the results open routes toward Josephson valves, spin-polarized supercurrents, and quantum computing architectures based on Andreev or Majorana states. Crucially, the effect requires only a single spin-split superconductor, simplifying device design and establishing EuS/Al heterostructures as a promising platform for hybrid quantum physics. [Full Article]
